path: root/arch/x86/include/asm/processor.h
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authorOleg Nesterov <>2012-09-03 15:24:17 +0200
committerAnton Arapov <>2012-10-29 11:23:45 +0100
commit8b5e7bd2a7d4aff576d50051d9da139a6cf67de3 (patch)
tree8bf40a9b247343847099fe7cf7821a5355da30b7 /arch/x86/include/asm/processor.h
parent06650b7b504327d3ffd53bc0867e8eff3f79b86c (diff)
uprobes/x86: Do not (ab)use TIF_SINGLESTEP/user_*_single_step() for single-stepping
user_enable/disable_single_step() was designed for ptrace, it assumes a single user and does unnecessary and wrong things for uprobes. For example: - arch_uprobe_enable_step() can't trust TIF_SINGLESTEP, an application itself can set X86_EFLAGS_TF which must be preserved after arch_uprobe_disable_step(). - we do not want to set TIF_SINGLESTEP/TIF_FORCED_TF in arch_uprobe_enable_step(), this only makes sense for ptrace. - otoh we leak TIF_SINGLESTEP if arch_uprobe_disable_step() doesn't do user_disable_single_step(), the application will be killed after the next syscall. - arch_uprobe_enable_step() does access_process_vm() we do not need/want. Change arch_uprobe_enable/disable_step() to set/clear X86_EFLAGS_TF directly, this is much simpler and more correct. However, we need to clear TIF_BLOCKSTEP/DEBUGCTLMSR_BTF before executing the probed insn, add set_task_blockstep(false). Note: with or without this patch, there is another (hopefully minor) problem. A probed "pushf" insn can see the wrong X86_EFLAGS_TF set by uprobes. Perhaps we should change _disable to update the stack, or teach arch_uprobe_skip_sstep() to emulate this insn. Signed-off-by: Oleg Nesterov <> Acked-by: Srikar Dronamraju <>
Diffstat (limited to 'arch/x86/include/asm/processor.h')
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index d048cad9bca..433d2e5c98a 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -759,6 +759,8 @@ static inline void update_debugctlmsr(unsigned long debugctlmsr)
wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctlmsr);
+extern void set_task_blockstep(struct task_struct *task, bool on);
* from system description table in BIOS. Mostly for MCA use, but
* others may find it useful: