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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@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Kyle Huey <me@kylehuey.com> Link: https://lore.kernel.org/r/20201027093608.028952500@infradead.org
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1 changed files with 6 additions and 6 deletions
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@ -793,12 +793,6 @@ static __always_inline unsigned long debug_read_clear_dr6(void)
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set_debugreg(DR6_RESERVED, 6);
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dr6 ^= DR6_RESERVED; /* Flip to positive polarity */
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/*
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* Clear the virtual DR6 value, ptrace routines will set bits here for
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* things we want signals for.
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*/
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current->thread.virtual_dr6 = 0;
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return dr6;
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}
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@ -942,6 +936,12 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
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irqentry_enter_from_user_mode(regs);
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instrumentation_begin();
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/*
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* Clear the virtual DR6 value, ptrace() routines will set bits here
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* for things it wants signals for.
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*/
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current->thread.virtual_dr6 = 0;
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/*
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* The SDM says "The processor clears the BTF flag when it
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* generates a debug exception." Clear TIF_BLOCKSTEP to keep
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