Commit-ID: 81edd9f69a6fd214fdbe66b43de6aa1610c84c63 Gitweb: http://git.kernel.org/tip/81edd9f69a6fd214fdbe66b43de6aa1610c84c63 Author: Andy Lutomirski <[email protected]> AuthorDate: Wed, 9 Mar 2016 19:00:28 -0800 Committer: Ingo Molnar <[email protected]> CommitDate: Thu, 10 Mar 2016 09:48:13 +0100
x86/entry/traps: Clear TIF_BLOCKSTEP on all debug exceptions The SDM says that debug exceptions clear BTF, and we need to keep TIF_BLOCKSTEP in sync with BTF. Clear it unconditionally and improve the comment. I suspect that the fact that kmemcheck could cause TIF_BLOCKSTEP not to be cleared was just an oversight. Signed-off-by: Andy Lutomirski <[email protected]> Cc: Andrew Cooper <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/fa86e55d196e6dde5b38839595bde2a292c52fdc.1457578375.git.l...@kernel.org Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/kernel/traps.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 410e8e2..1af5621 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -598,6 +598,13 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) dr6 &= ~DR6_RESERVED; /* + * The SDM says "The processor clears the BTF flag when it + * generates a debug exception." Clear TIF_BLOCKSTEP to keep + * TIF_BLOCKSTEP in sync with the hardware BTF flag. + */ + clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP); + + /* * If dr6 has no reason to give us about the origin of this trap, * then it's very likely the result of an icebp/int01 trap. * User wants a sigtrap for that. @@ -612,11 +619,6 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) /* DR6 may or may not be cleared by the CPU */ set_debugreg(0, 6); - /* - * The processor cleared BTF, so don't mark that we need it set. - */ - clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP); - /* Store the virtualized DR6 value */ tsk->thread.debugreg6 = dr6;
