Messages in this thread Patch in this message | | | Date | Tue, 27 Oct 2020 10:15:07 +0100 | From | Peter Zijlstra <> | Subject | [PATCH 3/3] x86/debug: Fix PTRACE_{BLOCK,SINGLE}STEP vs ptrace_get_debugreg(6) |
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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 we lost DR_STEP for 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> --- arch/x86/include/asm/ptrace.h | 2 ++ arch/x86/kernel/step.c | 9 +++++++++ arch/x86/kernel/traps.c | 2 +- 3 files changed, 12 insertions(+), 1 deletion(-)
--- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -355,6 +355,8 @@ static inline unsigned long regs_get_ker #define arch_has_block_step() (boot_cpu_data.x86 >= 6) #endif +extern unsigned long user_dr_step(unsigned long dr6); + #define ARCH_HAS_USER_SINGLE_STEP_REPORT struct user_desc; --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -235,3 +235,12 @@ void user_disable_single_step(struct tas if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF)) task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; } + +unsigned long user_dr_step(unsigned long dr6) +{ + if (test_thread_flag(TIF_BLOCKSTEP) || + test_thread_flag(TIF_SINGLESTEP)) + return dr6 & DR_STEP; + + return 0; +} --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -940,7 +940,7 @@ static __always_inline void exc_debug_us * Clear the virtual DR6 value, ptrace() routines will set bits here * for things it wants signals for. */ - current->thread.virtual_dr6 = 0; + current->thread.virtual_dr6 = user_dr_step(dr6); /* * The SDM says "The processor clears the BTF flag when it
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