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Subject[PATCH 6/7] uprobes: Xol should send SIGTRAP if X86_EFLAGS_TF was set
arch_uprobe_disable_step() correctly preserves X86_EFLAGS_TF and
returns to user-mode. But this means the application gets SIGTRAP
only after the next insn.

This means that UPROBE_CLEAR_TF logic is not really right. _enable
should only record the state of X86_EFLAGS_TF, and _disable should
check it separately from UPROBE_FIX_SETF.

Remove arch_uprobe_task->restore_flags, add ->saved_tf instead, and
change enable/disable accordingly.

arch_uprobe_skip_sstep() logic has the same problem, change it to
check X86_EFLAGS_TF and send SIGTRAP as well. We will cleanup this
all after we fold enable/disable_step into pre/post_hol hooks.

Note: send_sig(SIGTRAP) is not actually right, we need send_sigtrap().
But this needs more changes, handle_swbp() does the same and this is
equally wrong.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
arch/x86/include/asm/uprobes.h | 3 +--
arch/x86/kernel/uprobes.c | 19 +++++++++++++------
2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index cee5862..d561ff5 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -46,8 +46,7 @@ struct arch_uprobe_task {
#ifdef CONFIG_X86_64
unsigned long saved_scratch_register;
#endif
-#define UPROBE_CLEAR_TF (1 << 0)
- unsigned int restore_flags;
+ unsigned int saved_tf;
};

extern int arch_uprobe_analyze_insn(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long addr);
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 3b4aae6..7e993d1 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -653,7 +653,7 @@ void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
* Skip these instructions as per the currently known x86 ISA.
* 0x66* { 0x90 | 0x0f 0x1f | 0x0f 0x19 | 0x87 0xc0 }
*/
-bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
+static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
int i;

@@ -681,16 +681,21 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
return false;
}

+bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+ bool ret = __skip_sstep(auprobe, regs);
+ if (ret && (regs->flags & X86_EFLAGS_TF))
+ send_sig(SIGTRAP, current, 0);
+ return ret;
+}
+
void arch_uprobe_enable_step(struct arch_uprobe *auprobe)
{
struct task_struct *task = current;
struct arch_uprobe_task *autask = &task->utask->autask;
struct pt_regs *regs = task_pt_regs(task);

- autask->restore_flags = 0;
- if (!(regs->flags & X86_EFLAGS_TF) &&
- !(auprobe->fixups & UPROBE_FIX_SETF))
- autask->restore_flags |= UPROBE_CLEAR_TF;
+ autask->saved_tf = !!(regs->flags & X86_EFLAGS_TF);

regs->flags |= X86_EFLAGS_TF;
if (test_tsk_thread_flag(task, TIF_BLOCKSTEP))
@@ -707,6 +712,8 @@ void arch_uprobe_disable_step(struct arch_uprobe *auprobe)
* SIGTRAP if we do not clear TF. We need to examine the opcode to
* make it right.
*/
- if (autask->restore_flags & UPROBE_CLEAR_TF)
+ if (autask->saved_tf)
+ send_sig(SIGTRAP, task, 0);
+ else if (!(auprobe->fixups & UPROBE_FIX_SETF))
regs->flags &= ~X86_EFLAGS_TF;
}
--
1.5.5.1


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