linux/arch/x86/kernel/unwind_orc.c
Josh Poimboeuf 187b96db5c x86/unwind/orc: Fix unwind_get_return_address_ptr() for inactive tasks
Normally, show_trace_log_lvl() scans the stack, looking for text
addresses to print.  In parallel, it unwinds the stack with
unwind_next_frame().  If the stack address matches the pointer returned
by unwind_get_return_address_ptr() for the current frame, the text
address is printed normally without a question mark.  Otherwise it's
considered a breadcrumb (potentially from a previous call path) and it's
printed with a question mark to indicate that the address is unreliable
and typically can be ignored.

Since the following commit:

  f1d9a2abff ("x86/unwind/orc: Don't skip the first frame for inactive tasks")

... for inactive tasks, show_trace_log_lvl() prints *only* unreliable
addresses (prepended with '?').

That happens because, for the first frame of an inactive task,
unwind_get_return_address_ptr() returns the wrong return address
pointer: one word *below* the task stack pointer.  show_trace_log_lvl()
starts scanning at the stack pointer itself, so it never finds the first
'reliable' address, causing only guesses to being printed.

The first frame of an inactive task isn't a normal stack frame.  It's
actually just an instance of 'struct inactive_task_frame' which is left
behind by __switch_to_asm().  Now that this inactive frame is actually
exposed to callers, fix unwind_get_return_address_ptr() to interpret it
properly.

Fixes: f1d9a2abff ("x86/unwind/orc: Don't skip the first frame for inactive tasks")
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200522135435.vbxs7umku5pyrdbk@treble
2020-05-22 19:55:17 +02:00

708 lines
18 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/sort.h>
#include <asm/ptrace.h>
#include <asm/stacktrace.h>
#include <asm/unwind.h>
#include <asm/orc_types.h>
#include <asm/orc_lookup.h>
#define orc_warn(fmt, ...) \
printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)
#define orc_warn_current(args...) \
({ \
if (state->task == current) \
orc_warn(args); \
})
extern int __start_orc_unwind_ip[];
extern int __stop_orc_unwind_ip[];
extern struct orc_entry __start_orc_unwind[];
extern struct orc_entry __stop_orc_unwind[];
static bool orc_init __ro_after_init;
static unsigned int lookup_num_blocks __ro_after_init;
static inline unsigned long orc_ip(const int *ip)
{
return (unsigned long)ip + *ip;
}
static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
unsigned int num_entries, unsigned long ip)
{
int *first = ip_table;
int *last = ip_table + num_entries - 1;
int *mid = first, *found = first;
if (!num_entries)
return NULL;
/*
* Do a binary range search to find the rightmost duplicate of a given
* starting address. Some entries are section terminators which are
* "weak" entries for ensuring there are no gaps. They should be
* ignored when they conflict with a real entry.
*/
while (first <= last) {
mid = first + ((last - first) / 2);
if (orc_ip(mid) <= ip) {
found = mid;
first = mid + 1;
} else
last = mid - 1;
}
return u_table + (found - ip_table);
}
#ifdef CONFIG_MODULES
static struct orc_entry *orc_module_find(unsigned long ip)
{
struct module *mod;
mod = __module_address(ip);
if (!mod || !mod->arch.orc_unwind || !mod->arch.orc_unwind_ip)
return NULL;
return __orc_find(mod->arch.orc_unwind_ip, mod->arch.orc_unwind,
mod->arch.num_orcs, ip);
}
#else
static struct orc_entry *orc_module_find(unsigned long ip)
{
return NULL;
}
#endif
#ifdef CONFIG_DYNAMIC_FTRACE
static struct orc_entry *orc_find(unsigned long ip);
/*
* Ftrace dynamic trampolines do not have orc entries of their own.
* But they are copies of the ftrace entries that are static and
* defined in ftrace_*.S, which do have orc entries.
*
* If the unwinder comes across a ftrace trampoline, then find the
* ftrace function that was used to create it, and use that ftrace
* function's orc entry, as the placement of the return code in
* the stack will be identical.
*/
static struct orc_entry *orc_ftrace_find(unsigned long ip)
{
struct ftrace_ops *ops;
unsigned long caller;
ops = ftrace_ops_trampoline(ip);
if (!ops)
return NULL;
if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
caller = (unsigned long)ftrace_regs_call;
else
caller = (unsigned long)ftrace_call;
/* Prevent unlikely recursion */
if (ip == caller)
return NULL;
return orc_find(caller);
}
#else
static struct orc_entry *orc_ftrace_find(unsigned long ip)
{
return NULL;
}
#endif
/*
* If we crash with IP==0, the last successfully executed instruction
* was probably an indirect function call with a NULL function pointer,
* and we don't have unwind information for NULL.
* This hardcoded ORC entry for IP==0 allows us to unwind from a NULL function
* pointer into its parent and then continue normally from there.
*/
static struct orc_entry null_orc_entry = {
.sp_offset = sizeof(long),
.sp_reg = ORC_REG_SP,
.bp_reg = ORC_REG_UNDEFINED,
.type = ORC_TYPE_CALL
};
/* Fake frame pointer entry -- used as a fallback for generated code */
static struct orc_entry orc_fp_entry = {
.type = ORC_TYPE_CALL,
.sp_reg = ORC_REG_BP,
.sp_offset = 16,
.bp_reg = ORC_REG_PREV_SP,
.bp_offset = -16,
.end = 0,
};
static struct orc_entry *orc_find(unsigned long ip)
{
static struct orc_entry *orc;
if (ip == 0)
return &null_orc_entry;
/* For non-init vmlinux addresses, use the fast lookup table: */
if (ip >= LOOKUP_START_IP && ip < LOOKUP_STOP_IP) {
unsigned int idx, start, stop;
idx = (ip - LOOKUP_START_IP) / LOOKUP_BLOCK_SIZE;
if (unlikely((idx >= lookup_num_blocks-1))) {
orc_warn("WARNING: bad lookup idx: idx=%u num=%u ip=%pB\n",
idx, lookup_num_blocks, (void *)ip);
return NULL;
}
start = orc_lookup[idx];
stop = orc_lookup[idx + 1] + 1;
if (unlikely((__start_orc_unwind + start >= __stop_orc_unwind) ||
(__start_orc_unwind + stop > __stop_orc_unwind))) {
orc_warn("WARNING: bad lookup value: idx=%u num=%u start=%u stop=%u ip=%pB\n",
idx, lookup_num_blocks, start, stop, (void *)ip);
return NULL;
}
return __orc_find(__start_orc_unwind_ip + start,
__start_orc_unwind + start, stop - start, ip);
}
/* vmlinux .init slow lookup: */
if (init_kernel_text(ip))
return __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
__stop_orc_unwind_ip - __start_orc_unwind_ip, ip);
/* Module lookup: */
orc = orc_module_find(ip);
if (orc)
return orc;
return orc_ftrace_find(ip);
}
#ifdef CONFIG_MODULES
static DEFINE_MUTEX(sort_mutex);
static int *cur_orc_ip_table = __start_orc_unwind_ip;
static struct orc_entry *cur_orc_table = __start_orc_unwind;
static void orc_sort_swap(void *_a, void *_b, int size)
{
struct orc_entry *orc_a, *orc_b;
struct orc_entry orc_tmp;
int *a = _a, *b = _b, tmp;
int delta = _b - _a;
/* Swap the .orc_unwind_ip entries: */
tmp = *a;
*a = *b + delta;
*b = tmp - delta;
/* Swap the corresponding .orc_unwind entries: */
orc_a = cur_orc_table + (a - cur_orc_ip_table);
orc_b = cur_orc_table + (b - cur_orc_ip_table);
orc_tmp = *orc_a;
*orc_a = *orc_b;
*orc_b = orc_tmp;
}
static int orc_sort_cmp(const void *_a, const void *_b)
{
struct orc_entry *orc_a;
const int *a = _a, *b = _b;
unsigned long a_val = orc_ip(a);
unsigned long b_val = orc_ip(b);
if (a_val > b_val)
return 1;
if (a_val < b_val)
return -1;
/*
* The "weak" section terminator entries need to always be on the left
* to ensure the lookup code skips them in favor of real entries.
* These terminator entries exist to handle any gaps created by
* whitelisted .o files which didn't get objtool generation.
*/
orc_a = cur_orc_table + (a - cur_orc_ip_table);
return orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end ? -1 : 1;
}
void unwind_module_init(struct module *mod, void *_orc_ip, size_t orc_ip_size,
void *_orc, size_t orc_size)
{
int *orc_ip = _orc_ip;
struct orc_entry *orc = _orc;
unsigned int num_entries = orc_ip_size / sizeof(int);
WARN_ON_ONCE(orc_ip_size % sizeof(int) != 0 ||
orc_size % sizeof(*orc) != 0 ||
num_entries != orc_size / sizeof(*orc));
/*
* The 'cur_orc_*' globals allow the orc_sort_swap() callback to
* associate an .orc_unwind_ip table entry with its corresponding
* .orc_unwind entry so they can both be swapped.
*/
mutex_lock(&sort_mutex);
cur_orc_ip_table = orc_ip;
cur_orc_table = orc;
sort(orc_ip, num_entries, sizeof(int), orc_sort_cmp, orc_sort_swap);
mutex_unlock(&sort_mutex);
mod->arch.orc_unwind_ip = orc_ip;
mod->arch.orc_unwind = orc;
mod->arch.num_orcs = num_entries;
}
#endif
void __init unwind_init(void)
{
size_t orc_ip_size = (void *)__stop_orc_unwind_ip - (void *)__start_orc_unwind_ip;
size_t orc_size = (void *)__stop_orc_unwind - (void *)__start_orc_unwind;
size_t num_entries = orc_ip_size / sizeof(int);
struct orc_entry *orc;
int i;
if (!num_entries || orc_ip_size % sizeof(int) != 0 ||
orc_size % sizeof(struct orc_entry) != 0 ||
num_entries != orc_size / sizeof(struct orc_entry)) {
orc_warn("WARNING: Bad or missing .orc_unwind table. Disabling unwinder.\n");
return;
}
/*
* Note, the orc_unwind and orc_unwind_ip tables were already
* sorted at build time via the 'sorttable' tool.
* It's ready for binary search straight away, no need to sort it.
*/
/* Initialize the fast lookup table: */
lookup_num_blocks = orc_lookup_end - orc_lookup;
for (i = 0; i < lookup_num_blocks-1; i++) {
orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
num_entries,
LOOKUP_START_IP + (LOOKUP_BLOCK_SIZE * i));
if (!orc) {
orc_warn("WARNING: Corrupt .orc_unwind table. Disabling unwinder.\n");
return;
}
orc_lookup[i] = orc - __start_orc_unwind;
}
/* Initialize the ending block: */
orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind, num_entries,
LOOKUP_STOP_IP);
if (!orc) {
orc_warn("WARNING: Corrupt .orc_unwind table. Disabling unwinder.\n");
return;
}
orc_lookup[lookup_num_blocks-1] = orc - __start_orc_unwind;
orc_init = true;
}
unsigned long unwind_get_return_address(struct unwind_state *state)
{
if (unwind_done(state))
return 0;
return __kernel_text_address(state->ip) ? state->ip : 0;
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);
unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
{
struct task_struct *task = state->task;
if (unwind_done(state))
return NULL;
if (state->regs)
return &state->regs->ip;
if (task != current && state->sp == task->thread.sp) {
struct inactive_task_frame *frame = (void *)task->thread.sp;
return &frame->ret_addr;
}
if (state->sp)
return (unsigned long *)state->sp - 1;
return NULL;
}
static bool stack_access_ok(struct unwind_state *state, unsigned long _addr,
size_t len)
{
struct stack_info *info = &state->stack_info;
void *addr = (void *)_addr;
if (!on_stack(info, addr, len) &&
(get_stack_info(addr, state->task, info, &state->stack_mask)))
return false;
return true;
}
static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
unsigned long *val)
{
if (!stack_access_ok(state, addr, sizeof(long)))
return false;
*val = READ_ONCE_NOCHECK(*(unsigned long *)addr);
return true;
}
static bool deref_stack_regs(struct unwind_state *state, unsigned long addr,
unsigned long *ip, unsigned long *sp)
{
struct pt_regs *regs = (struct pt_regs *)addr;
/* x86-32 support will be more complicated due to the &regs->sp hack */
BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_32));
if (!stack_access_ok(state, addr, sizeof(struct pt_regs)))
return false;
*ip = regs->ip;
*sp = regs->sp;
return true;
}
static bool deref_stack_iret_regs(struct unwind_state *state, unsigned long addr,
unsigned long *ip, unsigned long *sp)
{
struct pt_regs *regs = (void *)addr - IRET_FRAME_OFFSET;
if (!stack_access_ok(state, addr, IRET_FRAME_SIZE))
return false;
*ip = regs->ip;
*sp = regs->sp;
return true;
}
/*
* If state->regs is non-NULL, and points to a full pt_regs, just get the reg
* value from state->regs.
*
* Otherwise, if state->regs just points to IRET regs, and the previous frame
* had full regs, it's safe to get the value from the previous regs. This can
* happen when early/late IRQ entry code gets interrupted by an NMI.
*/
static bool get_reg(struct unwind_state *state, unsigned int reg_off,
unsigned long *val)
{
unsigned int reg = reg_off/8;
if (!state->regs)
return false;
if (state->full_regs) {
*val = ((unsigned long *)state->regs)[reg];
return true;
}
if (state->prev_regs) {
*val = ((unsigned long *)state->prev_regs)[reg];
return true;
}
return false;
}
bool unwind_next_frame(struct unwind_state *state)
{
unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp;
enum stack_type prev_type = state->stack_info.type;
struct orc_entry *orc;
bool indirect = false;
if (unwind_done(state))
return false;
/* Don't let modules unload while we're reading their ORC data. */
preempt_disable();
/* End-of-stack check for user tasks: */
if (state->regs && user_mode(state->regs))
goto the_end;
/*
* Find the orc_entry associated with the text address.
*
* Decrement call return addresses by one so they work for sibling
* calls and calls to noreturn functions.
*/
orc = orc_find(state->signal ? state->ip : state->ip - 1);
if (!orc) {
/*
* As a fallback, try to assume this code uses a frame pointer.
* This is useful for generated code, like BPF, which ORC
* doesn't know about. This is just a guess, so the rest of
* the unwind is no longer considered reliable.
*/
orc = &orc_fp_entry;
state->error = true;
}
/* End-of-stack check for kernel threads: */
if (orc->sp_reg == ORC_REG_UNDEFINED) {
if (!orc->end)
goto err;
goto the_end;
}
/* Find the previous frame's stack: */
switch (orc->sp_reg) {
case ORC_REG_SP:
sp = state->sp + orc->sp_offset;
break;
case ORC_REG_BP:
sp = state->bp + orc->sp_offset;
break;
case ORC_REG_SP_INDIRECT:
sp = state->sp + orc->sp_offset;
indirect = true;
break;
case ORC_REG_BP_INDIRECT:
sp = state->bp + orc->sp_offset;
indirect = true;
break;
case ORC_REG_R10:
if (!get_reg(state, offsetof(struct pt_regs, r10), &sp)) {
orc_warn_current("missing R10 value at %pB\n",
(void *)state->ip);
goto err;
}
break;
case ORC_REG_R13:
if (!get_reg(state, offsetof(struct pt_regs, r13), &sp)) {
orc_warn_current("missing R13 value at %pB\n",
(void *)state->ip);
goto err;
}
break;
case ORC_REG_DI:
if (!get_reg(state, offsetof(struct pt_regs, di), &sp)) {
orc_warn_current("missing RDI value at %pB\n",
(void *)state->ip);
goto err;
}
break;
case ORC_REG_DX:
if (!get_reg(state, offsetof(struct pt_regs, dx), &sp)) {
orc_warn_current("missing DX value at %pB\n",
(void *)state->ip);
goto err;
}
break;
default:
orc_warn("unknown SP base reg %d at %pB\n",
orc->sp_reg, (void *)state->ip);
goto err;
}
if (indirect) {
if (!deref_stack_reg(state, sp, &sp))
goto err;
}
/* Find IP, SP and possibly regs: */
switch (orc->type) {
case ORC_TYPE_CALL:
ip_p = sp - sizeof(long);
if (!deref_stack_reg(state, ip_p, &state->ip))
goto err;
state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
state->ip, (void *)ip_p);
state->sp = sp;
state->regs = NULL;
state->prev_regs = NULL;
state->signal = false;
break;
case ORC_TYPE_REGS:
if (!deref_stack_regs(state, sp, &state->ip, &state->sp)) {
orc_warn_current("can't access registers at %pB\n",
(void *)orig_ip);
goto err;
}
state->regs = (struct pt_regs *)sp;
state->prev_regs = NULL;
state->full_regs = true;
state->signal = true;
break;
case ORC_TYPE_REGS_IRET:
if (!deref_stack_iret_regs(state, sp, &state->ip, &state->sp)) {
orc_warn_current("can't access iret registers at %pB\n",
(void *)orig_ip);
goto err;
}
if (state->full_regs)
state->prev_regs = state->regs;
state->regs = (void *)sp - IRET_FRAME_OFFSET;
state->full_regs = false;
state->signal = true;
break;
default:
orc_warn("unknown .orc_unwind entry type %d at %pB\n",
orc->type, (void *)orig_ip);
goto err;
}
/* Find BP: */
switch (orc->bp_reg) {
case ORC_REG_UNDEFINED:
if (get_reg(state, offsetof(struct pt_regs, bp), &tmp))
state->bp = tmp;
break;
case ORC_REG_PREV_SP:
if (!deref_stack_reg(state, sp + orc->bp_offset, &state->bp))
goto err;
break;
case ORC_REG_BP:
if (!deref_stack_reg(state, state->bp + orc->bp_offset, &state->bp))
goto err;
break;
default:
orc_warn("unknown BP base reg %d for ip %pB\n",
orc->bp_reg, (void *)orig_ip);
goto err;
}
/* Prevent a recursive loop due to bad ORC data: */
if (state->stack_info.type == prev_type &&
on_stack(&state->stack_info, (void *)state->sp, sizeof(long)) &&
state->sp <= prev_sp) {
orc_warn_current("stack going in the wrong direction? at %pB\n",
(void *)orig_ip);
goto err;
}
preempt_enable();
return true;
err:
state->error = true;
the_end:
preempt_enable();
state->stack_info.type = STACK_TYPE_UNKNOWN;
return false;
}
EXPORT_SYMBOL_GPL(unwind_next_frame);
void __unwind_start(struct unwind_state *state, struct task_struct *task,
struct pt_regs *regs, unsigned long *first_frame)
{
memset(state, 0, sizeof(*state));
state->task = task;
if (!orc_init)
goto err;
/*
* Refuse to unwind the stack of a task while it's executing on another
* CPU. This check is racy, but that's ok: the unwinder has other
* checks to prevent it from going off the rails.
*/
if (task_on_another_cpu(task))
goto err;
if (regs) {
if (user_mode(regs))
goto the_end;
state->ip = regs->ip;
state->sp = regs->sp;
state->bp = regs->bp;
state->regs = regs;
state->full_regs = true;
state->signal = true;
} else if (task == current) {
asm volatile("lea (%%rip), %0\n\t"
"mov %%rsp, %1\n\t"
"mov %%rbp, %2\n\t"
: "=r" (state->ip), "=r" (state->sp),
"=r" (state->bp));
} else {
struct inactive_task_frame *frame = (void *)task->thread.sp;
state->sp = task->thread.sp;
state->bp = READ_ONCE_NOCHECK(frame->bp);
state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
}
if (get_stack_info((unsigned long *)state->sp, state->task,
&state->stack_info, &state->stack_mask)) {
/*
* We weren't on a valid stack. It's possible that
* we overflowed a valid stack into a guard page.
* See if the next page up is valid so that we can
* generate some kind of backtrace if this happens.
*/
void *next_page = (void *)PAGE_ALIGN((unsigned long)state->sp);
state->error = true;
if (get_stack_info(next_page, state->task, &state->stack_info,
&state->stack_mask))
return;
}
/*
* The caller can provide the address of the first frame directly
* (first_frame) or indirectly (regs->sp) to indicate which stack frame
* to start unwinding at. Skip ahead until we reach it.
*/
/* When starting from regs, skip the regs frame: */
if (regs) {
unwind_next_frame(state);
return;
}
/* Otherwise, skip ahead to the user-specified starting frame: */
while (!unwind_done(state) &&
(!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
state->sp < (unsigned long)first_frame))
unwind_next_frame(state);
return;
err:
state->error = true;
the_end:
state->stack_info.type = STACK_TYPE_UNKNOWN;
}
EXPORT_SYMBOL_GPL(__unwind_start);