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From: Greg KH on 13 Aug 2010 17:50
2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

Based on commit 96054569190bdec375fe824e48ca1f4e3b53dd36 upstream,
authored by Linus Torvalds.

This is my backport to the .27 kernel tree, hopefully preserving
the same functionality.

Original commit message:
It's wrong for several reasons, but the most direct one is that the
fault may be for the stack accesses to set up a previous SIGBUS. When
we have a kernel exception, the kernel exception handler does all the
fixups, not some user-level signal handler.

Even apart from the nested SIGBUS issue, it's also wrong to give out
kernel fault addresses in the signal handler info block, or to send a
SIGBUS when a system call already returns EFAULT.

Cc: Linus Torvalds <torvalds(a)linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
arch/x86/mm/fault.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -589,6 +589,7 @@ void __kprobes do_page_fault(struct pt_r
unsigned long address;
int write, si_code;
int fault;
+ int should_exit_no_context = 0;
#ifdef CONFIG_X86_64
unsigned long flags;
#endif
@@ -876,6 +877,9 @@ no_context:
oops_end(flags, regs, SIGKILL);
#endif

+ if (should_exit_no_context)
+ return;
+
/*
* We ran out of memory, or some other thing happened to us that made
* us unable to handle the page fault gracefully.
@@ -901,8 +905,11 @@ do_sigbus:
up_read(&mm->mmap_sem);

/* Kernel mode? Handle exceptions or die */
- if (!(error_code & PF_USER))
+ if (!(error_code & PF_USER)) {
+ should_exit_no_context = 1;
goto no_context;
+ }
+
#ifdef CONFIG_X86_32
/* User space => ok to do another page fault */
if (is_prefetch(regs, address, error_code))


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