Messages in this thread Patch in this message | | | Date | Tue, 27 Oct 2020 10:15:06 +0100 | From | Peter Zijlstra <> | Subject | [PATCH 2/3] x86/debug: Only clear/set ->virtual_dr6 for userspace #DB |
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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@infradead.org> --- arch/x86/kernel/traps.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
--- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -793,12 +793,6 @@ static __always_inline unsigned long deb 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_us 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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