x86/unwind: Ensure stack grows down

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@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20161027131058.tpdffwlqipv7pcd6@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 5639db619c03b53e545a61141804a1d975f2e3cf..ea7b7f9a3b9e29c891509429f55238e17dcdc66c 100644 (file)
--- 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;
@@ -79,6 +88,7 @@ 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;
@@ -142,6 +152,15 @@ 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;
@@ -154,10 +173,17 @@ bool unwind_next_frame(struct unwind_state *state)
        return true;
 
 bad_address:
-       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);
+       if (state->regs) {
+               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_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_frame);
+       }
 the_end:
        state->stack_info.type = STACK_TYPE_UNKNOWN;
        return false;