diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2020-10-27 19:33:30 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-10-27 23:15:24 +0100 |
| commit | cb05143bdf428f280a5d519c82abf196d7871c11 (patch) | |
| tree | 6ef08abfc2e82060af40c487089dc549597949dc | |
| parent | a195f3d4528a2f88d6f986f6b1101775ad4891cf (diff) | |
x86/debug: Fix DR_STEP vs ptrace_get_debugreg(6)
Commit d53d9bc0cf78 ("x86/debug: Change thread.debugreg6 to
thread.virtual_dr6") changed the semantics of the variable from random
collection of bits, to exactly only those bits that ptrace() needs.
Unfortunately this lost DR_STEP for PTRACE_{BLOCK,SINGLE}STEP.
Furthermore, it turns out that userspace expects DR_STEP to be
unconditionally available, even for manual TF usage outside of
PTRACE_{BLOCK,SINGLE}_STEP.
Fixes: d53d9bc0cf78 ("x86/debug: Change thread.debugreg6 to thread.virtual_dr6")
Reported-by: Kyle Huey <me@kylehuey.com>
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/20201027183330.GM2628@hirez.programming.kicks-ass.net
| -rw-r--r-- | arch/x86/kernel/traps.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 32b2d39272e0..e19df6cde35d 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -937,10 +937,13 @@ 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. + * Start the virtual/ptrace DR6 value with just the DR_STEP mask + * of the real DR6. ptrace_triggered() will set the DR_TRAPn bits. + * + * Userspace expects DR_STEP to be visible in ptrace_get_debugreg(6) + * even if it is not the result of PTRACE_SINGLESTEP. */ - current->thread.virtual_dr6 = 0; + current->thread.virtual_dr6 = (dr6 & DR_STEP); /* * The SDM says "The processor clears the BTF flag when it |