x86: don't send SIGBUS for kernel page faults

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@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 33842556ce70828eaabf88854ca25fede937667e..9d3c576a6b2e85f0d14a3073a6745d6af2df60db 100644 (file)
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -589,6 +589,7 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
        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))