From: Andy Lutomirski Date: Thu, 10 Mar 2016 03:00:28 +0000 (-0800) Subject: x86/entry/traps: Clear TIF_BLOCKSTEP on all debug exceptions X-Git-Tag: v4.13~3498^2~11 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=81edd9f69a6fd214fdbe66b43de6aa1610c84c63;p=mirror_ubuntu-bionic-kernel.git 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 Cc: Andrew Cooper Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/fa86e55d196e6dde5b38839595bde2a292c52fdc.1457578375.git.luto@kernel.org Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 410e8e2700c5..1af56217fb5d 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -597,6 +597,13 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) /* Filter out all the reserved bits which are preset to 1 */ 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. @@ -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;