diff options
| author | Andy Lutomirski <luto@kernel.org> | 2016-03-09 19:00:29 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2016-03-10 09:48:13 +0100 |
| commit | 8bb5643686d2898bec181c407651cf84e77d413f (patch) | |
| tree | fffaba109deef6957634a64d7830c2214b9d652d /arch | |
| parent | 81edd9f69a6fd214fdbe66b43de6aa1610c84c63 (diff) | |
x86/entry/traps: Clear DR6 early in do_debug() and improve the comment
Leaving any bits set in DR6 on return from a debug exception is
asking for trouble. Prevent it by writing zero right away and
clarify the comment.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andy Lutomirski <luto@amacapital.net>
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: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/3857676e1be8fb27db4b89bbb1e2052b7f435ff4.1457578375.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/traps.c | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 1af56217fb5d..7394be8b1a66 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -593,6 +593,18 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) ist_enter(regs); get_debugreg(dr6, 6); + /* + * The Intel SDM says: + * + * Certain debug exceptions may clear bits 0-3. The remaining + * contents of the DR6 register are never cleared by the + * processor. To avoid confusion in identifying debug + * exceptions, debug handlers should clear the register before + * returning to the interrupted task. + * + * Keep it simple: clear DR6 immediately. + */ + set_debugreg(0, 6); /* Filter out all the reserved bits which are preset to 1 */ dr6 &= ~DR6_RESERVED; @@ -616,9 +628,6 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) if ((dr6 & DR_STEP) && kmemcheck_trap(regs)) goto exit; - /* DR6 may or may not be cleared by the CPU */ - set_debugreg(0, 6); - /* Store the virtualized DR6 value */ tsk->thread.debugreg6 = dr6; |