linux/arch/x86/kernel/process_64.c

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/*
* Copyright (C) 1995 Linus Torvalds
*
* Pentium III FXSR, SSE support
* Gareth Hughes <gareth@valinux.com>, May 2000
*
* X86-64 port
* Andi Kleen.
*
* CPU hotplug support - ashok.raj@intel.com
*/
/*
* This file handles the architecture-dependent parts of process handling..
*/
#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/elfcore.h>
#include <linux/smp.h>
#include <linux/slab.h>
#include <linux/user.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/notifier.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/prctl.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <linux/ftrace.h>
#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/i387.h>
#include <asm/fpu-internal.h>
#include <asm/mmu_context.h>
#include <asm/prctl.h>
#include <asm/desc.h>
#include <asm/proto.h>
#include <asm/ia32.h>
#include <asm/idle.h>
#include <asm/syscalls.h>
#include <asm/debugreg.h>
#include <asm/switch_to.h>
asmlinkage extern void ret_from_fork(void);
DEFINE_PER_CPU(unsigned long, old_rsp);
/* Prints also some state that isn't saved in the pt_regs */
void __show_regs(struct pt_regs *regs, int all)
{
unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
unsigned long d0, d1, d2, d3, d6, d7;
unsigned int fsindex, gsindex;
unsigned int ds, cs, es;
printk(KERN_DEFAULT "RIP: %04lx:[<%016lx>] ", regs->cs & 0xffff, regs->ip);
printk_address(regs->ip, 1);
printk(KERN_DEFAULT "RSP: %04lx:%016lx EFLAGS: %08lx\n", regs->ss,
regs->sp, regs->flags);
printk(KERN_DEFAULT "RAX: %016lx RBX: %016lx RCX: %016lx\n",
regs->ax, regs->bx, regs->cx);
printk(KERN_DEFAULT "RDX: %016lx RSI: %016lx RDI: %016lx\n",
regs->dx, regs->si, regs->di);
printk(KERN_DEFAULT "RBP: %016lx R08: %016lx R09: %016lx\n",
regs->bp, regs->r8, regs->r9);
printk(KERN_DEFAULT "R10: %016lx R11: %016lx R12: %016lx\n",
regs->r10, regs->r11, regs->r12);
printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
regs->r13, regs->r14, regs->r15);
asm("movl %%ds,%0" : "=r" (ds));
asm("movl %%cs,%0" : "=r" (cs));
asm("movl %%es,%0" : "=r" (es));
asm("movl %%fs,%0" : "=r" (fsindex));
asm("movl %%gs,%0" : "=r" (gsindex));
rdmsrl(MSR_FS_BASE, fs);
rdmsrl(MSR_GS_BASE, gs);
rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
if (!all)
return;
cr0 = read_cr0();
cr2 = read_cr2();
cr3 = read_cr3();
cr4 = read_cr4();
printk(KERN_DEFAULT "FS: %016lx(%04x) GS:%016lx(%04x) knlGS:%016lx\n",
fs, fsindex, gs, gsindex, shadowgs);
printk(KERN_DEFAULT "CS: %04x DS: %04x ES: %04x CR0: %016lx\n", cs, ds,
es, cr0);
printk(KERN_DEFAULT "CR2: %016lx CR3: %016lx CR4: %016lx\n", cr2, cr3,
cr4);
get_debugreg(d0, 0);
get_debugreg(d1, 1);
get_debugreg(d2, 2);
printk(KERN_DEFAULT "DR0: %016lx DR1: %016lx DR2: %016lx\n", d0, d1, d2);
get_debugreg(d3, 3);
get_debugreg(d6, 6);
get_debugreg(d7, 7);
printk(KERN_DEFAULT "DR3: %016lx DR6: %016lx DR7: %016lx\n", d3, d6, d7);
}
void release_thread(struct task_struct *dead_task)
{
if (dead_task->mm) {
if (dead_task->mm->context.size) {
pr_warn("WARNING: dead process %s still has LDT? <%p/%d>\n",
dead_task->comm,
dead_task->mm->context.ldt,
dead_task->mm->context.size);
BUG();
}
}
}
static inline void set_32bit_tls(struct task_struct *t, int tls, u32 addr)
{
struct user_desc ud = {
.base_addr = addr,
.limit = 0xfffff,
.seg_32bit = 1,
.limit_in_pages = 1,
.useable = 1,
};
struct desc_struct *desc = t->thread.tls_array;
desc += tls;
fill_ldt(desc, &ud);
}
static inline u32 read_32bit_tls(struct task_struct *t, int tls)
{
return get_desc_base(&t->thread.tls_array[tls]);
}
int copy_thread(unsigned long clone_flags, unsigned long sp,
unsigned long arg, struct task_struct *p)
{
int err;
struct pt_regs *childregs;
struct task_struct *me = current;
p->thread.sp0 = (unsigned long)task_stack_page(p) + THREAD_SIZE;
childregs = task_pt_regs(p);
p->thread.sp = (unsigned long) childregs;
p->thread.usersp = me->thread.usersp;
set_tsk_thread_flag(p, TIF_FORK);
p->fpu_counter = 0;
p->thread.io_bitmap_ptr = NULL;
savesegment(gs, p->thread.gsindex);
p->thread.gs = p->thread.gsindex ? 0 : me->thread.gs;
savesegment(fs, p->thread.fsindex);
p->thread.fs = p->thread.fsindex ? 0 : me->thread.fs;
savesegment(es, p->thread.es);
savesegment(ds, p->thread.ds);
memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
if (unlikely(p->flags & PF_KTHREAD)) {
/* kernel thread */
memset(childregs, 0, sizeof(struct pt_regs));
childregs->sp = (unsigned long)childregs;
childregs->ss = __KERNEL_DS;
childregs->bx = sp; /* function */
childregs->bp = arg;
childregs->orig_ax = -1;
childregs->cs = __KERNEL_CS | get_kernel_rpl();
childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_BIT1;
return 0;
}
*childregs = *current_pt_regs();
childregs->ax = 0;
if (sp)
childregs->sp = sp;
err = -ENOMEM;
hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events This patch rebase the implementation of the breakpoints API on top of perf events instances. Each breakpoints are now perf events that handle the register scheduling, thread/cpu attachment, etc.. The new layering is now made as follows: ptrace kgdb ftrace perf syscall \ | / / \ | / / / Core breakpoint API / / | / | / Breakpoints perf events | | Breakpoints PMU ---- Debug Register constraints handling (Part of core breakpoint API) | | Hardware debug registers Reasons of this rewrite: - Use the centralized/optimized pmu registers scheduling, implying an easier arch integration - More powerful register handling: perf attributes (pinned/flexible events, exclusive/non-exclusive, tunable period, etc...) Impact: - New perf ABI: the hardware breakpoints counters - Ptrace breakpoints setting remains tricky and still needs some per thread breakpoints references. Todo (in the order): - Support breakpoints perf counter events for perf tools (ie: implement perf_bpcounter_event()) - Support from perf tools Changes in v2: - Follow the perf "event " rename - The ptrace regression have been fixed (ptrace breakpoint perf events weren't released when a task ended) - Drop the struct hw_breakpoint and store generic fields in perf_event_attr. - Separate core and arch specific headers, drop asm-generic/hw_breakpoint.h and create linux/hw_breakpoint.h - Use new generic len/type for breakpoint - Handle off case: when breakpoints api is not supported by an arch Changes in v3: - Fix broken CONFIG_KVM, we need to propagate the breakpoint api changes to kvm when we exit the guest and restore the bp registers to the host. Changes in v4: - Drop the hw_breakpoint_restore() stub as it is only used by KVM - EXPORT_SYMBOL_GPL hw_breakpoint_restore() as KVM can be built as a module - Restore the breakpoints unconditionally on kvm guest exit: TIF_DEBUG_THREAD doesn't anymore cover every cases of running breakpoints and vcpu->arch.switch_db_regs might not always be set when the guest used debug registers. (Waiting for a reliable optimization) Changes in v5: - Split-up the asm-generic/hw-breakpoint.h moving to linux/hw_breakpoint.h into a separate patch - Optimize the breakpoints restoring while switching from kvm guest to host. We only want to restore the state if we have active breakpoints to the host, otherwise we don't care about messed-up address registers. - Add asm/hw_breakpoint.h to Kbuild - Fix bad breakpoint type in trace_selftest.c Changes in v6: - Fix wrong header inclusion in trace.h (triggered a build error with CONFIG_FTRACE_SELFTEST Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Prasad <prasad@linux.vnet.ibm.com> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Jan Kiszka <jan.kiszka@web.de> Cc: Jiri Slaby <jirislaby@gmail.com> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Avi Kivity <avi@redhat.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Masami Hiramatsu <mhiramat@redhat.com> Cc: Paul Mundt <lethal@linux-sh.org>
2009-09-09 17:22:48 +00:00
memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
p->thread.io_bitmap_ptr = kmemdup(me->thread.io_bitmap_ptr,
IO_BITMAP_BYTES, GFP_KERNEL);
if (!p->thread.io_bitmap_ptr) {
p->thread.io_bitmap_max = 0;
return -ENOMEM;
}
set_tsk_thread_flag(p, TIF_IO_BITMAP);
}
/*
* Set a new TLS for the child thread?
*/
if (clone_flags & CLONE_SETTLS) {
#ifdef CONFIG_IA32_EMULATION
if (test_thread_flag(TIF_IA32))
err = do_set_thread_area(p, -1,
(struct user_desc __user *)childregs->si, 0);
else
#endif
err = do_arch_prctl(p, ARCH_SET_FS, childregs->r8);
if (err)
goto out;
}
err = 0;
out:
if (err && p->thread.io_bitmap_ptr) {
kfree(p->thread.io_bitmap_ptr);
p->thread.io_bitmap_max = 0;
}
return err;
}
static void
start_thread_common(struct pt_regs *regs, unsigned long new_ip,
unsigned long new_sp,
unsigned int _cs, unsigned int _ss, unsigned int _ds)
{
loadsegment(fs, 0);
loadsegment(es, _ds);
loadsegment(ds, _ds);
load_gs_index(0);
current->thread.usersp = new_sp;
regs->ip = new_ip;
regs->sp = new_sp;
this_cpu_write(old_rsp, new_sp);
regs->cs = _cs;
regs->ss = _ss;
regs->flags = X86_EFLAGS_IF;
}
void
start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
{
start_thread_common(regs, new_ip, new_sp,
__USER_CS, __USER_DS, 0);
}
#ifdef CONFIG_IA32_EMULATION
void start_thread_ia32(struct pt_regs *regs, u32 new_ip, u32 new_sp)
{
start_thread_common(regs, new_ip, new_sp,
test_thread_flag(TIF_X32)
? __USER_CS : __USER32_CS,
__USER_DS, __USER_DS);
}
#endif
/*
* switch_to(x,y) should switch tasks from x to y.
*
* This could still be optimized:
* - fold all the options into a flag word and test it with a single test.
* - could test fs/gs bitsliced
*
* Kprobes not supported here. Set the probe on schedule instead.
* Function graph tracer not supported too.
*/
__notrace_funcgraph struct task_struct *
__switch_to(struct task_struct *prev_p, struct task_struct *next_p)
{
struct thread_struct *prev = &prev_p->thread;
struct thread_struct *next = &next_p->thread;
int cpu = smp_processor_id();
struct tss_struct *tss = &per_cpu(init_tss, cpu);
unsigned fsindex, gsindex;
i387: re-introduce FPU state preloading at context switch time After all the FPU state cleanups and finally finding the problem that caused all our FPU save/restore problems, this re-introduces the preloading of FPU state that was removed in commit b3b0870ef3ff ("i387: do not preload FPU state at task switch time"). However, instead of simply reverting the removal, this reimplements preloading with several fixes, most notably - properly abstracted as a true FPU state switch, rather than as open-coded save and restore with various hacks. In particular, implementing it as a proper FPU state switch allows us to optimize the CR0.TS flag accesses: there is no reason to set the TS bit only to then almost immediately clear it again. CR0 accesses are quite slow and expensive, don't flip the bit back and forth for no good reason. - Make sure that the same model works for both x86-32 and x86-64, so that there are no gratuitous differences between the two due to the way they save and restore segment state differently due to architectural differences that really don't matter to the FPU state. - Avoid exposing the "preload" state to the context switch routines, and in particular allow the concept of lazy state restore: if nothing else has used the FPU in the meantime, and the process is still on the same CPU, we can avoid restoring state from memory entirely, just re-expose the state that is still in the FPU unit. That optimized lazy restore isn't actually implemented here, but the infrastructure is set up for it. Of course, older CPU's that use 'fnsave' to save the state cannot take advantage of this, since the state saving also trashes the state. In other words, there is now an actual _design_ to the FPU state saving, rather than just random historical baggage. Hopefully it's easier to follow as a result. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-02-18 20:56:35 +00:00
fpu_switch_t fpu;
i387: support lazy restore of FPU state This makes us recognize when we try to restore FPU state that matches what we already have in the FPU on this CPU, and avoids the restore entirely if so. To do this, we add two new data fields: - a percpu 'fpu_owner_task' variable that gets written any time we update the "has_fpu" field, and thus acts as a kind of back-pointer to the task that owns the CPU. The exception is when we save the FPU state as part of a context switch - if the save can keep the FPU state around, we leave the 'fpu_owner_task' variable pointing at the task whose FP state still remains on the CPU. - a per-thread 'last_cpu' field, that indicates which CPU that thread used its FPU on last. We update this on every context switch (writing an invalid CPU number if the last context switch didn't leave the FPU in a lazily usable state), so we know that *that* thread has done nothing else with the FPU since. These two fields together can be used when next switching back to the task to see if the CPU still matches: if 'fpu_owner_task' matches the task we are switching to, we know that no other task (or kernel FPU usage) touched the FPU on this CPU in the meantime, and if the current CPU number matches the 'last_cpu' field, we know that this thread did no other FP work on any other CPU, so the FPU state on the CPU must match what was saved on last context switch. In that case, we can avoid the 'f[x]rstor' entirely, and just clear the CR0.TS bit. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-02-19 21:27:00 +00:00
fpu = switch_fpu_prepare(prev_p, next_p, cpu);
/*
* Reload esp0, LDT and the page table pointer:
*/
load_sp0(tss, next);
/*
* Switch DS and ES.
* This won't pick up thread selector changes, but I guess that is ok.
*/
savesegment(es, prev->es);
if (unlikely(next->es | prev->es))
loadsegment(es, next->es);
savesegment(ds, prev->ds);
if (unlikely(next->ds | prev->ds))
loadsegment(ds, next->ds);
/* We must save %fs and %gs before load_TLS() because
* %fs and %gs may be cleared by load_TLS().
*
* (e.g. xen_load_tls())
*/
savesegment(fs, fsindex);
savesegment(gs, gsindex);
load_TLS(next, cpu);
/*
* Leave lazy mode, flushing any hypercalls made here.
* This must be done before restoring TLS segments so
* the GDT and LDT are properly updated, and must be
* done before math_state_restore, so the TS bit is up
* to date.
*/
arch_end_context_switch(next_p);
/*
* Switch FS and GS.
*
* Segment register != 0 always requires a reload. Also
* reload when it has changed. When prev process used 64bit
* base always reload to avoid an information leak.
*/
if (unlikely(fsindex | next->fsindex | prev->fs)) {
loadsegment(fs, next->fsindex);
/*
* Check if the user used a selector != 0; if yes
* clear 64bit base, since overloaded base is always
* mapped to the Null selector
*/
if (fsindex)
prev->fs = 0;
}
/* when next process has a 64bit base use it */
if (next->fs)
wrmsrl(MSR_FS_BASE, next->fs);
prev->fsindex = fsindex;
if (unlikely(gsindex | next->gsindex | prev->gs)) {
load_gs_index(next->gsindex);
if (gsindex)
prev->gs = 0;
}
if (next->gs)
wrmsrl(MSR_KERNEL_GS_BASE, next->gs);
prev->gsindex = gsindex;
i387: re-introduce FPU state preloading at context switch time After all the FPU state cleanups and finally finding the problem that caused all our FPU save/restore problems, this re-introduces the preloading of FPU state that was removed in commit b3b0870ef3ff ("i387: do not preload FPU state at task switch time"). However, instead of simply reverting the removal, this reimplements preloading with several fixes, most notably - properly abstracted as a true FPU state switch, rather than as open-coded save and restore with various hacks. In particular, implementing it as a proper FPU state switch allows us to optimize the CR0.TS flag accesses: there is no reason to set the TS bit only to then almost immediately clear it again. CR0 accesses are quite slow and expensive, don't flip the bit back and forth for no good reason. - Make sure that the same model works for both x86-32 and x86-64, so that there are no gratuitous differences between the two due to the way they save and restore segment state differently due to architectural differences that really don't matter to the FPU state. - Avoid exposing the "preload" state to the context switch routines, and in particular allow the concept of lazy state restore: if nothing else has used the FPU in the meantime, and the process is still on the same CPU, we can avoid restoring state from memory entirely, just re-expose the state that is still in the FPU unit. That optimized lazy restore isn't actually implemented here, but the infrastructure is set up for it. Of course, older CPU's that use 'fnsave' to save the state cannot take advantage of this, since the state saving also trashes the state. In other words, there is now an actual _design_ to the FPU state saving, rather than just random historical baggage. Hopefully it's easier to follow as a result. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-02-18 20:56:35 +00:00
switch_fpu_finish(next_p, fpu);
/*
* Switch the PDA and FPU contexts.
*/
prev->usersp = this_cpu_read(old_rsp);
this_cpu_write(old_rsp, next->usersp);
this_cpu_write(current_task, next_p);
this_cpu_write(kernel_stack,
(unsigned long)task_stack_page(next_p) +
THREAD_SIZE - KERNEL_STACK_OFFSET);
/*
* Now maybe reload the debug registers and handle I/O bitmaps
*/
if (unlikely(task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT ||
task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
__switch_to_xtra(prev_p, next_p, tss);
return prev_p;
}
void set_personality_64bit(void)
{
/* inherit personality from parent */
/* Make sure to be in 64bit mode */
clear_thread_flag(TIF_IA32);
clear_thread_flag(TIF_ADDR32);
clear_thread_flag(TIF_X32);
/* Ensure the corresponding mm is not marked. */
if (current->mm)
current->mm->context.ia32_compat = 0;
/* TBD: overwrites user setup. Should have two bits.
But 64bit processes have always behaved this way,
so it's not too bad. The main problem is just that
32bit childs are affected again. */
current->personality &= ~READ_IMPLIES_EXEC;
}
void set_personality_ia32(bool x32)
{
/* inherit personality from parent */
/* Make sure to be in 32bit mode */
set_thread_flag(TIF_ADDR32);
/* Mark the associated mm as containing 32-bit tasks. */
if (current->mm)
current->mm->context.ia32_compat = 1;
if (x32) {
clear_thread_flag(TIF_IA32);
set_thread_flag(TIF_X32);
current->personality &= ~READ_IMPLIES_EXEC;
/* is_compat_task() uses the presence of the x32
syscall bit flag to determine compat status */
current_thread_info()->status &= ~TS_COMPAT;
} else {
set_thread_flag(TIF_IA32);
clear_thread_flag(TIF_X32);
current->personality |= force_personality32;
/* Prepare the first "return" to user space */
current_thread_info()->status |= TS_COMPAT;
}
}
EXPORT_SYMBOL_GPL(set_personality_ia32);
unsigned long get_wchan(struct task_struct *p)
{
unsigned long stack;
u64 fp, ip;
int count = 0;
if (!p || p == current || p->state == TASK_RUNNING)
return 0;
stack = (unsigned long)task_stack_page(p);
if (p->thread.sp < stack || p->thread.sp >= stack+THREAD_SIZE)
return 0;
fp = *(u64 *)(p->thread.sp);
do {
if (fp < (unsigned long)stack ||
fp >= (unsigned long)stack+THREAD_SIZE)
return 0;
ip = *(u64 *)(fp+8);
if (!in_sched_functions(ip))
return ip;
fp = *(u64 *)fp;
} while (count++ < 16);
return 0;
}
long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
{
int ret = 0;
int doit = task == current;
int cpu;
switch (code) {
case ARCH_SET_GS:
if (addr >= TASK_SIZE_OF(task))
return -EPERM;
cpu = get_cpu();
/* handle small bases via the GDT because that's faster to
switch. */
if (addr <= 0xffffffff) {
set_32bit_tls(task, GS_TLS, addr);
if (doit) {
load_TLS(&task->thread, cpu);
load_gs_index(GS_TLS_SEL);
}
task->thread.gsindex = GS_TLS_SEL;
task->thread.gs = 0;
} else {
task->thread.gsindex = 0;
task->thread.gs = addr;
if (doit) {
load_gs_index(0);
ret = wrmsrl_safe(MSR_KERNEL_GS_BASE, addr);
}
}
put_cpu();
break;
case ARCH_SET_FS:
/* Not strictly needed for fs, but do it for symmetry
with gs */
if (addr >= TASK_SIZE_OF(task))
return -EPERM;
cpu = get_cpu();
/* handle small bases via the GDT because that's faster to
switch. */
if (addr <= 0xffffffff) {
set_32bit_tls(task, FS_TLS, addr);
if (doit) {
load_TLS(&task->thread, cpu);
loadsegment(fs, FS_TLS_SEL);
}
task->thread.fsindex = FS_TLS_SEL;
task->thread.fs = 0;
} else {
task->thread.fsindex = 0;
task->thread.fs = addr;
if (doit) {
/* set the selector to 0 to not confuse
__switch_to */
loadsegment(fs, 0);
ret = wrmsrl_safe(MSR_FS_BASE, addr);
}
}
put_cpu();
break;
case ARCH_GET_FS: {
unsigned long base;
if (task->thread.fsindex == FS_TLS_SEL)
base = read_32bit_tls(task, FS_TLS);
else if (doit)
rdmsrl(MSR_FS_BASE, base);
else
base = task->thread.fs;
ret = put_user(base, (unsigned long __user *)addr);
break;
}
case ARCH_GET_GS: {
unsigned long base;
[PATCH] x86_64: Plug GS leak in arch_prctl() In linux-2.6.16, we have noticed a problem where the gs base value returned from an arch_prtcl(ARCH_GET_GS, ...) call will be incorrect if: - the current/calling task has NOT set its own gs base yet to a non-zero value, - some other task that ran on the same processor previously set their own gs base to a non-zero value. In this situation, the ARCH_GET_GS code will read and return the MSR_KERNEL_GS_BASE msr register. However, since the __switch_to() code does NOT load/zero the MSR_KERNEL_GS_BASE register when the task that is switched IN has a zero next->gs value, the caller of arch_prctl(ARCH_GET_GS, ...) will get back the value of some previous tasks's gs base value instead of 0. Change the arch_prctl() ARCH_GET_GS code to only read and return the MSR_KERNEL_GS_BASE msr register if the 'gs' register of the calling task is non-zero. Side note: Since in addition to using arch_prctl(ARCH_SET_GS, ...), a task can also setup a gs base value by using modify_ldt() and write an index value into 'gs' from user space, the patch below reads 'gs' instead of using thread.gs, since in the modify_ldt() case, the thread.gs value will be 0, and incorrect value would be returned (the task->thread.gs value). When the user has not set its own gs base value and the 'gs' register is zero, then the MSR_KERNEL_GS_BASE register will not be read and a value of zero will be returned by reading and returning 'task->thread.gs'. The first patch shown below is an attempt at implementing this approach. Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-04-07 17:50:25 +00:00
unsigned gsindex;
if (task->thread.gsindex == GS_TLS_SEL)
base = read_32bit_tls(task, GS_TLS);
[PATCH] x86_64: Plug GS leak in arch_prctl() In linux-2.6.16, we have noticed a problem where the gs base value returned from an arch_prtcl(ARCH_GET_GS, ...) call will be incorrect if: - the current/calling task has NOT set its own gs base yet to a non-zero value, - some other task that ran on the same processor previously set their own gs base to a non-zero value. In this situation, the ARCH_GET_GS code will read and return the MSR_KERNEL_GS_BASE msr register. However, since the __switch_to() code does NOT load/zero the MSR_KERNEL_GS_BASE register when the task that is switched IN has a zero next->gs value, the caller of arch_prctl(ARCH_GET_GS, ...) will get back the value of some previous tasks's gs base value instead of 0. Change the arch_prctl() ARCH_GET_GS code to only read and return the MSR_KERNEL_GS_BASE msr register if the 'gs' register of the calling task is non-zero. Side note: Since in addition to using arch_prctl(ARCH_SET_GS, ...), a task can also setup a gs base value by using modify_ldt() and write an index value into 'gs' from user space, the patch below reads 'gs' instead of using thread.gs, since in the modify_ldt() case, the thread.gs value will be 0, and incorrect value would be returned (the task->thread.gs value). When the user has not set its own gs base value and the 'gs' register is zero, then the MSR_KERNEL_GS_BASE register will not be read and a value of zero will be returned by reading and returning 'task->thread.gs'. The first patch shown below is an attempt at implementing this approach. Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-04-07 17:50:25 +00:00
else if (doit) {
savesegment(gs, gsindex);
[PATCH] x86_64: Plug GS leak in arch_prctl() In linux-2.6.16, we have noticed a problem where the gs base value returned from an arch_prtcl(ARCH_GET_GS, ...) call will be incorrect if: - the current/calling task has NOT set its own gs base yet to a non-zero value, - some other task that ran on the same processor previously set their own gs base to a non-zero value. In this situation, the ARCH_GET_GS code will read and return the MSR_KERNEL_GS_BASE msr register. However, since the __switch_to() code does NOT load/zero the MSR_KERNEL_GS_BASE register when the task that is switched IN has a zero next->gs value, the caller of arch_prctl(ARCH_GET_GS, ...) will get back the value of some previous tasks's gs base value instead of 0. Change the arch_prctl() ARCH_GET_GS code to only read and return the MSR_KERNEL_GS_BASE msr register if the 'gs' register of the calling task is non-zero. Side note: Since in addition to using arch_prctl(ARCH_SET_GS, ...), a task can also setup a gs base value by using modify_ldt() and write an index value into 'gs' from user space, the patch below reads 'gs' instead of using thread.gs, since in the modify_ldt() case, the thread.gs value will be 0, and incorrect value would be returned (the task->thread.gs value). When the user has not set its own gs base value and the 'gs' register is zero, then the MSR_KERNEL_GS_BASE register will not be read and a value of zero will be returned by reading and returning 'task->thread.gs'. The first patch shown below is an attempt at implementing this approach. Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-04-07 17:50:25 +00:00
if (gsindex)
rdmsrl(MSR_KERNEL_GS_BASE, base);
else
base = task->thread.gs;
} else
base = task->thread.gs;
ret = put_user(base, (unsigned long __user *)addr);
break;
}
default:
ret = -EINVAL;
break;
}
return ret;
}
long sys_arch_prctl(int code, unsigned long addr)
{
return do_arch_prctl(current, code, addr);
}
unsigned long KSTK_ESP(struct task_struct *task)
{
return (test_tsk_thread_flag(task, TIF_IA32)) ?
(task_pt_regs(task)->sp) : ((task)->thread.usersp);
}