[PATCH v4 51/57] x86/unwind: warn if stack grows up

From: Josh Poimboeuf
Date: Thu Aug 18 2016 - 09:11:26 EST


Add a sanity check to ensure the stack only grows down, and print a
warning if the check fails.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
arch/x86/kernel/unwind_frame.c | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 4dbdf4f..140dac4 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -32,6 +32,15 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);

+static size_t regs_size(struct pt_regs *regs)
+{
+ /* x86_32 regs from kernel mode are two words shorter */
+ if (IS_ENABLED(CONFIG_X86_32) && !user_mode(regs))
+ return sizeof(*regs) - (2*sizeof(long));
+
+ return sizeof(*regs);
+}
+
static bool is_last_task_frame(struct unwind_state *state)
{
unsigned long bp = (unsigned long)state->bp;
@@ -86,6 +95,7 @@ bool unwind_next_frame(struct unwind_state *state)
struct pt_regs *regs;
unsigned long *next_bp, *next_frame;
size_t next_len;
+ enum stack_type prev_type = state->stack_info.type;

if (unwind_done(state))
return false;
@@ -149,6 +159,18 @@ bool unwind_next_frame(struct unwind_state *state)
goto bad_address;
}

+ /* make sure it only unwinds up and doesn't overlap the last frame */
+ if (state->stack_info.type == prev_type) {
+ if (state->regs &&
+ (void *)next_frame < (void *)state->regs +
+ regs_size(state->regs))
+ goto bad_address;
+
+ if (state->bp &&
+ (void *)next_frame < (void *)state->bp + FRAME_HEADER_SIZE)
+ goto bad_address;
+ }
+
/* move to the next frame */
if (regs) {
state->regs = regs;
@@ -165,12 +187,12 @@ bad_address:
printk_deferred_once(KERN_WARNING
"WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
state->regs, state->task->comm,
- state->task->pid, next_bp);
+ state->task->pid, next_frame);
else
printk_deferred_once(KERN_WARNING
"WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
state->bp, state->task->comm,
- state->task->pid, next_bp);
+ state->task->pid, next_frame);
the_end:
state->stack_info.type = STACK_TYPE_UNKNOWN;
return false;
--
2.7.4