[PATCH 1/1] uprobes/x86: Fix the wrong ->si_addr when xol triggers a trap

[Oleg Nesterov]

If the probed insn triggers a trap, ->si_addr = regs->ip is technically
correct, but this is not what the signal handler wants; we need to pass
the address of the probed insn, not the address of xol slot.

Add the new arch-agnostic helper, uprobe_get_trap_addr(), and change
fill_trap_info() and math_error() to use it. !CONFIG_UPROBES case in
uprobes.h uses a macro to avoid include hell and ensure that it can be
compiled even if an architecture doesn't define instruction_pointer().

Test-case:

	#include <signal.h>
	#include <stdio.h>
	#include <unistd.h>

	extern void probe_div(void);

	void sigh(int sig, siginfo_t *info, void *c)
	{
		int passed = (info->si_addr == probe_div);
		printf(passed ? "PASS\n" : "FAIL\n");
		_exit(!passed);
	}

	int main(void)
	{
		struct sigaction sa = {
			.sa_sigaction	= sigh,
			.sa_flags	= SA_SIGINFO,
		};

		sigaction(SIGFPE, &sa, NULL);

		asm (
			"xor %ecx,%ecx\n"
			".globl probe_div; probe_div:\n"
			"idiv %ecx\n"
		);

		return 0;
	}

it fails if probe_div() is probed.

Note: show_unhandled_signals users should probably use this helper too,
but we need to cleanup them first.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 arch/x86/kernel/traps.c |    7 ++++---
 include/linux/uprobes.h |    4 ++++
 kernel/events/uprobes.c |   10 ++++++++++
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 73b3ea3..3fdb205 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -23,6 +23,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/ptrace.h>
+#include <linux/uprobes.h>
 #include <linux/string.h>
 #include <linux/delay.h>
 #include <linux/errno.h>
@@ -148,11 +149,11 @@ static siginfo_t *fill_trap_info(struct pt_regs *regs, int signr, int trapnr,
 
 	case X86_TRAP_DE:
 		sicode = FPE_INTDIV;
-		siaddr = regs->ip;
+		siaddr = uprobe_get_trap_addr(regs);
 		break;
 	case X86_TRAP_UD:
 		sicode = ILL_ILLOPN;
-		siaddr = regs->ip;
+		siaddr = uprobe_get_trap_addr(regs);
 		break;
 	case X86_TRAP_AC:
 		sicode = BUS_ADRALN;
@@ -531,7 +532,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 	task->thread.error_code = error_code;
 	info.si_signo = SIGFPE;
 	info.si_errno = 0;
-	info.si_addr = (void __user *)regs->ip;
+	info.si_addr = (void __user *)uprobe_get_trap_addr(regs);
 	if (trapnr == X86_TRAP_MF) {
 		unsigned short cwd, swd;
 		/*
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index edff2b9..88c3b7e 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -102,6 +102,7 @@ extern int __weak set_orig_insn(struct arch_uprobe *aup, struct mm_struct *mm, u
 extern bool __weak is_swbp_insn(uprobe_opcode_t *insn);
 extern bool __weak is_trap_insn(uprobe_opcode_t *insn);
 extern unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs);
+extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
 extern int uprobe_write_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_t);
 extern int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
 extern int uprobe_apply(struct inode *inode, loff_t offset, struct uprobe_consumer *uc, bool);
@@ -130,6 +131,9 @@ extern bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *r
 #else /* !CONFIG_UPROBES */
 struct uprobes_state {
 };
+
+#define uprobe_get_trap_addr(regs)	instruction_pointer(regs)
+
 static inline int
 uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
 {
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index a13251e..3b02c72 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1351,6 +1351,16 @@ unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs)
 	return instruction_pointer(regs) - UPROBE_SWBP_INSN_SIZE;
 }
 
+unsigned long uprobe_get_trap_addr(struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	if (unlikely(utask && utask->active_uprobe))
+		return utask->vaddr;
+
+	return instruction_pointer(regs);
+}
+
 /*
  * Called with no locks held.
  * Called in context of a exiting or a exec-ing thread.
-- 
1.5.5.1


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