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Commit 3a4664aa authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

uprobes/x86: 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. 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: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
parent 9bd1190a

arch/x86/include/asm/uprobes.h

+1 −2
Original line number Diff line number Diff line
@@ -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);

arch/x86/kernel/uprobes.c

+13 −6
Original line number Diff line number Diff line
@@ -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;

}