The following commit has been merged into the x86/urgent branch of tip: Commit-ID: a195f3d4528a2f88d6f986f6b1101775ad4891cf Gitweb: https://git.kernel.org/tip/a195f3d4528a2f88d6f986f6b1101775ad4891cf Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Tue, 27 Oct 2020 10:15:06 +01:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Tue, 27 Oct 2020 23:15:23 +01:00 x86/debug: Only clear/set ->virtual_dr6 for userspace #DB The ->virtual_dr6 is the value used by ptrace_{get,set}_debugreg(6). A kernel #DB clearing it could mean spurious malfunction of ptrace() expectations. Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Tested-by: Kyle Huey <me@xxxxxxxxxxxx> Link: https://lore.kernel.org/r/20201027093608.028952500@xxxxxxxxxxxxx --- arch/x86/kernel/traps.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index b5208aa..32b2d39 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -793,12 +793,6 @@ static __always_inline unsigned long debug_read_clear_dr6(void) set_debugreg(DR6_RESERVED, 6); dr6 ^= DR6_RESERVED; /* Flip to positive polarity */ - /* - * Clear the virtual DR6 value, ptrace routines will set bits here for - * things we want signals for. - */ - current->thread.virtual_dr6 = 0; - return dr6; } @@ -943,6 +937,12 @@ static __always_inline void exc_debug_user(struct pt_regs *regs, instrumentation_begin(); /* + * Clear the virtual DR6 value, ptrace() routines will set bits here + * for things it wants signals for. + */ + current->thread.virtual_dr6 = 0; + + /* * 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.
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