From dbe3ed1c078c193be34326728d494c5c4bc115e2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds <torvalds@woody.linux-foundation.org> Date: Wed, 19 Sep 2007 11:37:14 -0700 Subject: [PATCH] x86-64: page faults from user mode are always user faults Randy Dunlap noticed an interesting "crashme" behaviour on his dual Prescott Xeon setup, where he gets page faults with the error code having a zero "user" bit, but the register state points back to user mode. This may be a CPU microcode buglet triggered by some strange instruction pattern that crashme generates, and loading a microcode update seems to possibly have fixed it. Regardless, we really should trust the register state more than the error code, since it's really the register state that determines whether we can actually send a signal, or whether we're in kernel mode and need to oops/kill the process in the case of a page fault. Cc: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> --- arch/x86_64/mm/fault.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86_64/mm/fault.c b/arch/x86_64/mm/fault.c index 327c9f2fa626..54816adb8e93 100644 --- a/arch/x86_64/mm/fault.c +++ b/arch/x86_64/mm/fault.c @@ -374,6 +374,13 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs, if (unlikely(in_atomic() || !mm)) goto bad_area_nosemaphore; + /* + * User-mode registers count as a user access even for any + * potential system fault or CPU buglet. + */ + if (user_mode_vm(regs)) + error_code |= PF_USER; + again: /* When running in the kernel we expect faults to occur only to * addresses in user space. All other faults represent errors in the -- GitLab