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uprobes/x86: Xol should send SIGTRAP if X86_EFLAGS_TF was set

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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. This assumes that the probed insn
was not trapped, see the next patch.

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>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
This commit is contained in:
Oleg Nesterov 2012-09-03 16:05:10 +02:00
parent 9bd1190a11
commit 3a4664aa83
2 changed files with 14 additions and 8 deletions
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3
arch/x86/include/asm/uprobes.h
View File

@ -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);

19
arch/x86/kernel/uprobes.c
View File

@ -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;
}