From: Frederic Weisbecker on
Ingo,

Please pull the perf/urgent branch that can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
perf/urgent

Thanks,
Frederic
---

Frederic Weisbecker (1):
perf: Fix unsafe frame rewinding with hot regs fetching


arch/x86/kernel/dumpstack.h | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)

---
commit ab285f2b5290d92b7ec1a6f9aad54308dadf6157
Author: Frederic Weisbecker <fweisbec(a)gmail.com>
Date: Thu Apr 8 14:05:50 2010 +0200

perf: Fix unsafe frame rewinding with hot regs fetching

When we fetch the hot regs and rewind to the nth caller, it
might happen that we dereference a frame pointer outside the
kernel stack boundaries, like in this example:

perf_trace_sched_switch+0xd5/0x120
schedule+0x6b5/0x860
retint_careful+0xd/0x21

Since we directly dereference a userspace frame pointer here while
rewinding behind retint_careful, this may end up in a crash.

Fix this by simply using probe_kernel_address() when we rewind the
frame pointer.

This issue will have a much more proper fix in the next version of the
perf_arch_fetch_caller_regs() API that will only need to rewind to the
first caller.

Reported-by: Eric Dumazet <eric.dumazet(a)gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec(a)gmail.com>
Tested-by: Eric Dumazet <eric.dumazet(a)gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra(a)chello.nl>
Cc: Arnaldo Carvalho de Melo <acme(a)redhat.com>
Cc: Paul Mackerras <paulus(a)samba.org>
Cc: David Miller <davem(a)davemloft.net>
Cc: Archs <linux-arch(a)vger.kernel.org>

diff --git a/arch/x86/kernel/dumpstack.h b/arch/x86/kernel/dumpstack.h
index e39e771..e1a93be 100644
--- a/arch/x86/kernel/dumpstack.h
+++ b/arch/x86/kernel/dumpstack.h
@@ -14,6 +14,8 @@
#define get_bp(bp) asm("movq %%rbp, %0" : "=r" (bp) :)
#endif

+#include <linux/uaccess.h>
+
extern void
show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
unsigned long *stack, unsigned long bp, char *log_lvl);
@@ -42,8 +44,10 @@ static inline unsigned long rewind_frame_pointer(int n)
get_bp(frame);

#ifdef CONFIG_FRAME_POINTER
- while (n--)
- frame = frame->next_frame;
+ while (n--) {
+ if (probe_kernel_address(&frame->next_frame, frame))
+ break;
+ }
#endif

return (unsigned long)frame;
--
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