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Subject[PATCH v7 3.2-rc2 27/30] uprobes: x86: introduce xol_was_trapped()

Postpone the signals until we execute the probed insn. This is
simply wrong if xol insn traps and generates the signal itself. Say,
SIGILL/SIGSEGV/etc.

Adds xol_was_trapped() to detect this case. It assumes that anything
like do_page_fault/do_trap/etc sets thread.trap_no != -1.

We add uprobe_task_arch_info->saved_trap_no and change
pre_xol/post_xol to save/restore thread.trap_no, xol_was_trapped()
simply checks that ->trap_no is not equal to UPROBE_TRAP_NO == -1
set by pre_xol().

Original-patch-from: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---

Changelog (since v6)
- added x86 specific hook for aborting xol.

arch/x86/include/asm/uprobes.h | 7 ++++++-
arch/x86/kernel/uprobes.c | 33 ++++++++++++++++++++++++++++++++-
2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 99d7d4b..6a47024 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -39,16 +39,21 @@ struct uprobe_arch_info {

struct uprobe_task_arch_info {
unsigned long saved_scratch_register;
+ unsigned long saved_trap_no;
};
#else
struct uprobe_arch_info {};
-struct uprobe_task_arch_info {};
+struct uprobe_task_arch_info {
+ unsigned long saved_trap_no;
+};
#endif
struct uprobe;
extern int analyze_insn(struct mm_struct *mm, struct uprobe *uprobe);
extern void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr);
extern int pre_xol(struct uprobe *uprobe, struct pt_regs *regs);
extern int post_xol(struct uprobe *uprobe, struct pt_regs *regs);
+extern bool xol_was_trapped(struct task_struct *tsk);
extern int uprobe_exception_notify(struct notifier_block *self,
unsigned long val, void *data);
+extern void abort_xol(struct pt_regs *regs, struct uprobe *uprobe);
#endif /* _ASM_UPROBES_H */
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 0792fc8..3f0eb4e 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -409,6 +409,8 @@ void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr)
regs->ip = vaddr;
}

+#define UPROBE_TRAP_NO -1ul
+
/*
* pre_xol - prepare to execute out of line.
* @uprobe: the probepoint information.
@@ -424,6 +426,9 @@ int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
{
struct uprobe_task_arch_info *tskinfo = &current->utask->tskinfo;

+ tskinfo->saved_trap_no = current->thread.trap_no;
+ current->thread.trap_no = UPROBE_TRAP_NO;
+
regs->ip = current->utask->xol_vaddr;
if (uprobe->fixups & UPROBES_FIX_RIP_AX) {
tskinfo->saved_scratch_register = regs->ax;
@@ -439,6 +444,11 @@ int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
#else
int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
{
+ struct uprobe_task_arch_info *tskinfo = &current->utask->tskinfo;
+
+ tskinfo->saved_trap_no = current->thread.trap_no;
+ current->thread.trap_no = UPROBE_TRAP_NO;
+
regs->ip = current->utask->xol_vaddr;
return 0;
}
@@ -494,7 +504,8 @@ static void handle_riprel_post_xol(struct uprobe *uprobe,
* Fall through to handle stuff like "jmpq *...(%rip)" and
* "callq *...(%rip)".
*/
- *correction += 4;
+ if (correction)
+ *correction += 4;
}
}
#else
@@ -504,6 +515,14 @@ static void handle_riprel_post_xol(struct uprobe *uprobe,
}
#endif

+bool xol_was_trapped(struct task_struct *tsk)
+{
+ if (tsk->thread.trap_no != UPROBE_TRAP_NO)
+ return true;
+
+ return false;
+}
+
/*
* Called after single-stepping. To avoid the SMP problems that can
* occur when we temporarily put back the original opcode to
@@ -534,6 +553,9 @@ int post_xol(struct uprobe *uprobe, struct pt_regs *regs)
int result = 0;
long correction;

+ WARN_ON_ONCE(current->thread.trap_no != UPROBE_TRAP_NO);
+
+ current->thread.trap_no = utask->tskinfo.saved_trap_no;
correction = (long)(utask->vaddr - utask->xol_vaddr);
handle_riprel_post_xol(uprobe, regs, &correction);
if (uprobe->fixups & UPROBES_FIX_IP)
@@ -571,3 +593,12 @@ int uprobe_exception_notify(struct notifier_block *self,
}
return ret;
}
+
+void abort_xol(struct pt_regs *regs, struct uprobe *uprobe)
+{
+ struct uprobe_task *utask = current->utask;
+
+ current->thread.trap_no = utask->tskinfo.saved_trap_no;
+ handle_riprel_post_xol(uprobe, regs, NULL);
+ set_instruction_pointer(regs, utask->vaddr);
+}


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