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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
---
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
