linux/arch/arm/kernel/signal.c
Jonathan Austin 9dfc28b630 ARM: mpu: protect the vectors page with an MPU region
Without an MMU it is possible for userspace programs to start executing code
in places that they have no business executing. The MPU allows some level of
protection against this.

This patch protects the vectors page from access by userspace processes.
Userspace tasks that dereference a null pointer are already protected by an
svc at 0x0 that kills them. However when tasks use an offset from a null
pointer (eg a function in a null struct) they miss this carefully placed svc
and enter the exception vectors in user mode, ending up in the kernel.

This patch causes programs that do this to receive a SEGV instead of happily
entering the kernel in user-mode, and hence avoid a 'Bad Mode' panic.

As part of this change it is necessary to make sigreturn happen via the
stack when there is not an sa_restorer function. This change is invisible to
userspace, and irrelevant to code compiled using a uClibc toolchain, which
always uses an sa_restorer function.

Because we don't get to remap the vectors in !MMU kuser_helpers are not
in a defined location, and hence aren't usable. This means we don't need to
worry about keeping them accessible from PL0

Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
CC: Nicolas Pitre <nico@linaro.org>
CC: Catalin Marinas <catalin.marinas@arm.com>
2013-06-17 15:13:18 +01:00

611 lines
16 KiB
C

/*
* linux/arch/arm/kernel/signal.c
*
* Copyright (C) 1995-2009 Russell King
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/uaccess.h>
#include <linux/tracehook.h>
#include <asm/elf.h>
#include <asm/cacheflush.h>
#include <asm/ucontext.h>
#include <asm/unistd.h>
#include <asm/vfp.h>
#include "signal.h"
/*
* For ARM syscalls, we encode the syscall number into the instruction.
*/
#define SWI_SYS_SIGRETURN (0xef000000|(__NR_sigreturn)|(__NR_OABI_SYSCALL_BASE))
#define SWI_SYS_RT_SIGRETURN (0xef000000|(__NR_rt_sigreturn)|(__NR_OABI_SYSCALL_BASE))
/*
* With EABI, the syscall number has to be loaded into r7.
*/
#define MOV_R7_NR_SIGRETURN (0xe3a07000 | (__NR_sigreturn - __NR_SYSCALL_BASE))
#define MOV_R7_NR_RT_SIGRETURN (0xe3a07000 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
/*
* For Thumb syscalls, we pass the syscall number via r7. We therefore
* need two 16-bit instructions.
*/
#define SWI_THUMB_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_sigreturn - __NR_SYSCALL_BASE))
#define SWI_THUMB_RT_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
const unsigned long sigreturn_codes[7] = {
MOV_R7_NR_SIGRETURN, SWI_SYS_SIGRETURN, SWI_THUMB_SIGRETURN,
MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
};
#ifdef CONFIG_CRUNCH
static int preserve_crunch_context(struct crunch_sigframe __user *frame)
{
char kbuf[sizeof(*frame) + 8];
struct crunch_sigframe *kframe;
/* the crunch context must be 64 bit aligned */
kframe = (struct crunch_sigframe *)((unsigned long)(kbuf + 8) & ~7);
kframe->magic = CRUNCH_MAGIC;
kframe->size = CRUNCH_STORAGE_SIZE;
crunch_task_copy(current_thread_info(), &kframe->storage);
return __copy_to_user(frame, kframe, sizeof(*frame));
}
static int restore_crunch_context(struct crunch_sigframe __user *frame)
{
char kbuf[sizeof(*frame) + 8];
struct crunch_sigframe *kframe;
/* the crunch context must be 64 bit aligned */
kframe = (struct crunch_sigframe *)((unsigned long)(kbuf + 8) & ~7);
if (__copy_from_user(kframe, frame, sizeof(*frame)))
return -1;
if (kframe->magic != CRUNCH_MAGIC ||
kframe->size != CRUNCH_STORAGE_SIZE)
return -1;
crunch_task_restore(current_thread_info(), &kframe->storage);
return 0;
}
#endif
#ifdef CONFIG_IWMMXT
static int preserve_iwmmxt_context(struct iwmmxt_sigframe *frame)
{
char kbuf[sizeof(*frame) + 8];
struct iwmmxt_sigframe *kframe;
/* the iWMMXt context must be 64 bit aligned */
kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
kframe->magic = IWMMXT_MAGIC;
kframe->size = IWMMXT_STORAGE_SIZE;
iwmmxt_task_copy(current_thread_info(), &kframe->storage);
return __copy_to_user(frame, kframe, sizeof(*frame));
}
static int restore_iwmmxt_context(struct iwmmxt_sigframe *frame)
{
char kbuf[sizeof(*frame) + 8];
struct iwmmxt_sigframe *kframe;
/* the iWMMXt context must be 64 bit aligned */
kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
if (__copy_from_user(kframe, frame, sizeof(*frame)))
return -1;
if (kframe->magic != IWMMXT_MAGIC ||
kframe->size != IWMMXT_STORAGE_SIZE)
return -1;
iwmmxt_task_restore(current_thread_info(), &kframe->storage);
return 0;
}
#endif
#ifdef CONFIG_VFP
static int preserve_vfp_context(struct vfp_sigframe __user *frame)
{
const unsigned long magic = VFP_MAGIC;
const unsigned long size = VFP_STORAGE_SIZE;
int err = 0;
__put_user_error(magic, &frame->magic, err);
__put_user_error(size, &frame->size, err);
if (err)
return -EFAULT;
return vfp_preserve_user_clear_hwstate(&frame->ufp, &frame->ufp_exc);
}
static int restore_vfp_context(struct vfp_sigframe __user *frame)
{
unsigned long magic;
unsigned long size;
int err = 0;
__get_user_error(magic, &frame->magic, err);
__get_user_error(size, &frame->size, err);
if (err)
return -EFAULT;
if (magic != VFP_MAGIC || size != VFP_STORAGE_SIZE)
return -EINVAL;
return vfp_restore_user_hwstate(&frame->ufp, &frame->ufp_exc);
}
#endif
/*
* Do a signal return; undo the signal stack. These are aligned to 64-bit.
*/
struct sigframe {
struct ucontext uc;
unsigned long retcode[2];
};
struct rt_sigframe {
struct siginfo info;
struct sigframe sig;
};
static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
{
struct aux_sigframe __user *aux;
sigset_t set;
int err;
err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
if (err == 0)
set_current_blocked(&set);
__get_user_error(regs->ARM_r0, &sf->uc.uc_mcontext.arm_r0, err);
__get_user_error(regs->ARM_r1, &sf->uc.uc_mcontext.arm_r1, err);
__get_user_error(regs->ARM_r2, &sf->uc.uc_mcontext.arm_r2, err);
__get_user_error(regs->ARM_r3, &sf->uc.uc_mcontext.arm_r3, err);
__get_user_error(regs->ARM_r4, &sf->uc.uc_mcontext.arm_r4, err);
__get_user_error(regs->ARM_r5, &sf->uc.uc_mcontext.arm_r5, err);
__get_user_error(regs->ARM_r6, &sf->uc.uc_mcontext.arm_r6, err);
__get_user_error(regs->ARM_r7, &sf->uc.uc_mcontext.arm_r7, err);
__get_user_error(regs->ARM_r8, &sf->uc.uc_mcontext.arm_r8, err);
__get_user_error(regs->ARM_r9, &sf->uc.uc_mcontext.arm_r9, err);
__get_user_error(regs->ARM_r10, &sf->uc.uc_mcontext.arm_r10, err);
__get_user_error(regs->ARM_fp, &sf->uc.uc_mcontext.arm_fp, err);
__get_user_error(regs->ARM_ip, &sf->uc.uc_mcontext.arm_ip, err);
__get_user_error(regs->ARM_sp, &sf->uc.uc_mcontext.arm_sp, err);
__get_user_error(regs->ARM_lr, &sf->uc.uc_mcontext.arm_lr, err);
__get_user_error(regs->ARM_pc, &sf->uc.uc_mcontext.arm_pc, err);
__get_user_error(regs->ARM_cpsr, &sf->uc.uc_mcontext.arm_cpsr, err);
err |= !valid_user_regs(regs);
aux = (struct aux_sigframe __user *) sf->uc.uc_regspace;
#ifdef CONFIG_CRUNCH
if (err == 0)
err |= restore_crunch_context(&aux->crunch);
#endif
#ifdef CONFIG_IWMMXT
if (err == 0 && test_thread_flag(TIF_USING_IWMMXT))
err |= restore_iwmmxt_context(&aux->iwmmxt);
#endif
#ifdef CONFIG_VFP
if (err == 0)
err |= restore_vfp_context(&aux->vfp);
#endif
return err;
}
asmlinkage int sys_sigreturn(struct pt_regs *regs)
{
struct sigframe __user *frame;
/* Always make any pending restarted system calls return -EINTR */
current_thread_info()->restart_block.fn = do_no_restart_syscall;
/*
* Since we stacked the signal on a 64-bit boundary,
* then 'sp' should be word aligned here. If it's
* not, then the user is trying to mess with us.
*/
if (regs->ARM_sp & 7)
goto badframe;
frame = (struct sigframe __user *)regs->ARM_sp;
if (!access_ok(VERIFY_READ, frame, sizeof (*frame)))
goto badframe;
if (restore_sigframe(regs, frame))
goto badframe;
return regs->ARM_r0;
badframe:
force_sig(SIGSEGV, current);
return 0;
}
asmlinkage int sys_rt_sigreturn(struct pt_regs *regs)
{
struct rt_sigframe __user *frame;
/* Always make any pending restarted system calls return -EINTR */
current_thread_info()->restart_block.fn = do_no_restart_syscall;
/*
* Since we stacked the signal on a 64-bit boundary,
* then 'sp' should be word aligned here. If it's
* not, then the user is trying to mess with us.
*/
if (regs->ARM_sp & 7)
goto badframe;
frame = (struct rt_sigframe __user *)regs->ARM_sp;
if (!access_ok(VERIFY_READ, frame, sizeof (*frame)))
goto badframe;
if (restore_sigframe(regs, &frame->sig))
goto badframe;
if (restore_altstack(&frame->sig.uc.uc_stack))
goto badframe;
return regs->ARM_r0;
badframe:
force_sig(SIGSEGV, current);
return 0;
}
static int
setup_sigframe(struct sigframe __user *sf, struct pt_regs *regs, sigset_t *set)
{
struct aux_sigframe __user *aux;
int err = 0;
__put_user_error(regs->ARM_r0, &sf->uc.uc_mcontext.arm_r0, err);
__put_user_error(regs->ARM_r1, &sf->uc.uc_mcontext.arm_r1, err);
__put_user_error(regs->ARM_r2, &sf->uc.uc_mcontext.arm_r2, err);
__put_user_error(regs->ARM_r3, &sf->uc.uc_mcontext.arm_r3, err);
__put_user_error(regs->ARM_r4, &sf->uc.uc_mcontext.arm_r4, err);
__put_user_error(regs->ARM_r5, &sf->uc.uc_mcontext.arm_r5, err);
__put_user_error(regs->ARM_r6, &sf->uc.uc_mcontext.arm_r6, err);
__put_user_error(regs->ARM_r7, &sf->uc.uc_mcontext.arm_r7, err);
__put_user_error(regs->ARM_r8, &sf->uc.uc_mcontext.arm_r8, err);
__put_user_error(regs->ARM_r9, &sf->uc.uc_mcontext.arm_r9, err);
__put_user_error(regs->ARM_r10, &sf->uc.uc_mcontext.arm_r10, err);
__put_user_error(regs->ARM_fp, &sf->uc.uc_mcontext.arm_fp, err);
__put_user_error(regs->ARM_ip, &sf->uc.uc_mcontext.arm_ip, err);
__put_user_error(regs->ARM_sp, &sf->uc.uc_mcontext.arm_sp, err);
__put_user_error(regs->ARM_lr, &sf->uc.uc_mcontext.arm_lr, err);
__put_user_error(regs->ARM_pc, &sf->uc.uc_mcontext.arm_pc, err);
__put_user_error(regs->ARM_cpsr, &sf->uc.uc_mcontext.arm_cpsr, err);
__put_user_error(current->thread.trap_no, &sf->uc.uc_mcontext.trap_no, err);
__put_user_error(current->thread.error_code, &sf->uc.uc_mcontext.error_code, err);
__put_user_error(current->thread.address, &sf->uc.uc_mcontext.fault_address, err);
__put_user_error(set->sig[0], &sf->uc.uc_mcontext.oldmask, err);
err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set));
aux = (struct aux_sigframe __user *) sf->uc.uc_regspace;
#ifdef CONFIG_CRUNCH
if (err == 0)
err |= preserve_crunch_context(&aux->crunch);
#endif
#ifdef CONFIG_IWMMXT
if (err == 0 && test_thread_flag(TIF_USING_IWMMXT))
err |= preserve_iwmmxt_context(&aux->iwmmxt);
#endif
#ifdef CONFIG_VFP
if (err == 0)
err |= preserve_vfp_context(&aux->vfp);
#endif
__put_user_error(0, &aux->end_magic, err);
return err;
}
static inline void __user *
get_sigframe(struct ksignal *ksig, struct pt_regs *regs, int framesize)
{
unsigned long sp = sigsp(regs->ARM_sp, ksig);
void __user *frame;
/*
* ATPCS B01 mandates 8-byte alignment
*/
frame = (void __user *)((sp - framesize) & ~7);
/*
* Check that we can actually write to the signal frame.
*/
if (!access_ok(VERIFY_WRITE, frame, framesize))
frame = NULL;
return frame;
}
/*
* translate the signal
*/
static inline int map_sig(int sig)
{
struct thread_info *thread = current_thread_info();
if (sig < 32 && thread->exec_domain && thread->exec_domain->signal_invmap)
sig = thread->exec_domain->signal_invmap[sig];
return sig;
}
static int
setup_return(struct pt_regs *regs, struct ksignal *ksig,
unsigned long __user *rc, void __user *frame)
{
unsigned long handler = (unsigned long)ksig->ka.sa.sa_handler;
unsigned long retcode;
int thumb = 0;
unsigned long cpsr = regs->ARM_cpsr & ~(PSR_f | PSR_E_BIT);
cpsr |= PSR_ENDSTATE;
/*
* Maybe we need to deliver a 32-bit signal to a 26-bit task.
*/
if (ksig->ka.sa.sa_flags & SA_THIRTYTWO)
cpsr = (cpsr & ~MODE_MASK) | USR_MODE;
#ifdef CONFIG_ARM_THUMB
if (elf_hwcap & HWCAP_THUMB) {
/*
* The LSB of the handler determines if we're going to
* be using THUMB or ARM mode for this signal handler.
*/
thumb = handler & 1;
if (thumb) {
cpsr |= PSR_T_BIT;
#if __LINUX_ARM_ARCH__ >= 7
/* clear the If-Then Thumb-2 execution state */
cpsr &= ~PSR_IT_MASK;
#endif
} else
cpsr &= ~PSR_T_BIT;
}
#endif
if (ksig->ka.sa.sa_flags & SA_RESTORER) {
retcode = (unsigned long)ksig->ka.sa.sa_restorer;
} else {
unsigned int idx = thumb << 1;
if (ksig->ka.sa.sa_flags & SA_SIGINFO)
idx += 3;
/*
* Put the sigreturn code on the stack no matter which return
* mechanism we use in order to remain ABI compliant
*/
if (__put_user(sigreturn_codes[idx], rc) ||
__put_user(sigreturn_codes[idx+1], rc+1))
return 1;
if ((cpsr & MODE32_BIT) && !IS_ENABLED(CONFIG_ARM_MPU)) {
/*
* 32-bit code can use the new high-page
* signal return code support except when the MPU has
* protected the vectors page from PL0
*/
retcode = KERN_SIGRETURN_CODE + (idx << 2) + thumb;
} else {
/*
* Ensure that the instruction cache sees
* the return code written onto the stack.
*/
flush_icache_range((unsigned long)rc,
(unsigned long)(rc + 2));
retcode = ((unsigned long)rc) + thumb;
}
}
regs->ARM_r0 = map_sig(ksig->sig);
regs->ARM_sp = (unsigned long)frame;
regs->ARM_lr = retcode;
regs->ARM_pc = handler;
regs->ARM_cpsr = cpsr;
return 0;
}
static int
setup_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
{
struct sigframe __user *frame = get_sigframe(ksig, regs, sizeof(*frame));
int err = 0;
if (!frame)
return 1;
/*
* Set uc.uc_flags to a value which sc.trap_no would never have.
*/
__put_user_error(0x5ac3c35a, &frame->uc.uc_flags, err);
err |= setup_sigframe(frame, regs, set);
if (err == 0)
err = setup_return(regs, ksig, frame->retcode, frame);
return err;
}
static int
setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
{
struct rt_sigframe __user *frame = get_sigframe(ksig, regs, sizeof(*frame));
int err = 0;
if (!frame)
return 1;
err |= copy_siginfo_to_user(&frame->info, &ksig->info);
__put_user_error(0, &frame->sig.uc.uc_flags, err);
__put_user_error(NULL, &frame->sig.uc.uc_link, err);
err |= __save_altstack(&frame->sig.uc.uc_stack, regs->ARM_sp);
err |= setup_sigframe(&frame->sig, regs, set);
if (err == 0)
err = setup_return(regs, ksig, frame->sig.retcode, frame);
if (err == 0) {
/*
* For realtime signals we must also set the second and third
* arguments for the signal handler.
* -- Peter Maydell <pmaydell@chiark.greenend.org.uk> 2000-12-06
*/
regs->ARM_r1 = (unsigned long)&frame->info;
regs->ARM_r2 = (unsigned long)&frame->sig.uc;
}
return err;
}
/*
* OK, we're invoking a handler
*/
static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
{
sigset_t *oldset = sigmask_to_save();
int ret;
/*
* Set up the stack frame
*/
if (ksig->ka.sa.sa_flags & SA_SIGINFO)
ret = setup_rt_frame(ksig, oldset, regs);
else
ret = setup_frame(ksig, oldset, regs);
/*
* Check that the resulting registers are actually sane.
*/
ret |= !valid_user_regs(regs);
signal_setup_done(ret, ksig, 0);
}
/*
* Note that 'init' is a special process: it doesn't get signals it doesn't
* want to handle. Thus you cannot kill init even with a SIGKILL even by
* mistake.
*
* Note that we go through the signals twice: once to check the signals that
* the kernel can handle, and then we build all the user-level signal handling
* stack-frames in one go after that.
*/
static int do_signal(struct pt_regs *regs, int syscall)
{
unsigned int retval = 0, continue_addr = 0, restart_addr = 0;
struct ksignal ksig;
int restart = 0;
/*
* If we were from a system call, check for system call restarting...
*/
if (syscall) {
continue_addr = regs->ARM_pc;
restart_addr = continue_addr - (thumb_mode(regs) ? 2 : 4);
retval = regs->ARM_r0;
/*
* Prepare for system call restart. We do this here so that a
* debugger will see the already changed PSW.
*/
switch (retval) {
case -ERESTART_RESTARTBLOCK:
restart -= 2;
case -ERESTARTNOHAND:
case -ERESTARTSYS:
case -ERESTARTNOINTR:
restart++;
regs->ARM_r0 = regs->ARM_ORIG_r0;
regs->ARM_pc = restart_addr;
break;
}
}
/*
* Get the signal to deliver. When running under ptrace, at this
* point the debugger may change all our registers ...
*/
/*
* Depending on the signal settings we may need to revert the
* decision to restart the system call. But skip this if a
* debugger has chosen to restart at a different PC.
*/
if (get_signal(&ksig)) {
/* handler */
if (unlikely(restart) && regs->ARM_pc == restart_addr) {
if (retval == -ERESTARTNOHAND ||
retval == -ERESTART_RESTARTBLOCK
|| (retval == -ERESTARTSYS
&& !(ksig.ka.sa.sa_flags & SA_RESTART))) {
regs->ARM_r0 = -EINTR;
regs->ARM_pc = continue_addr;
}
}
handle_signal(&ksig, regs);
} else {
/* no handler */
restore_saved_sigmask();
if (unlikely(restart) && regs->ARM_pc == restart_addr) {
regs->ARM_pc = continue_addr;
return restart;
}
}
return 0;
}
asmlinkage int
do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
{
do {
if (likely(thread_flags & _TIF_NEED_RESCHED)) {
schedule();
} else {
if (unlikely(!user_mode(regs)))
return 0;
local_irq_enable();
if (thread_flags & _TIF_SIGPENDING) {
int restart = do_signal(regs, syscall);
if (unlikely(restart)) {
/*
* Restart without handlers.
* Deal with it without leaving
* the kernel space.
*/
return restart;
}
syscall = 0;
} else {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
}
}
local_irq_disable();
thread_flags = current_thread_info()->flags;
} while (thread_flags & _TIF_WORK_MASK);
return 0;
}