Messages in this thread | | | From | Kyle Huey <> | Date | Tue, 27 Oct 2020 10:22:34 -0700 | Subject | Re: [PATCH 3/3] x86/debug: Fix PTRACE_{BLOCK,SINGLE}STEP vs ptrace_get_debugreg(6) |
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On Tue, Oct 27, 2020 at 2:44 AM Peter Zijlstra <peterz@infradead.org> wrote: > > 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 > >
Tested-by: Kyle Huey <me@kylehuey.com>
Confirmed that this patch series fixes rr when applied on top of the v5.10-rc1 tag.
- Kyle
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