linux-kernel - [tip: perf/core] uprobes/x86: Harden uretprobe syscall trampoline check

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Message-ID: <174126060240.14745.15365015848455636391.tip-bot2@tip-bot2>
Date: Thu, 06 Mar 2025 11:30:02 -0000
From: "tip-bot2 for Jiri Olsa" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Jann Horn <jannh@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 Ingo Molnar <mingo@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
 Kees Cook <kees@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>,
 Andy Lutomirski <luto@...nel.org>, stable@...r.kernel.org, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: perf/core] uprobes/x86: Harden uretprobe syscall trampoline check

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     fa6192adc32f4fdfe5b74edd5b210e12afd6ecc0
Gitweb:        https://git.kernel.org/tip/fa6192adc32f4fdfe5b74edd5b210e12afd6ecc0
Author:        Jiri Olsa <jolsa@...nel.org>
AuthorDate:    Wed, 12 Feb 2025 23:04:33 +01:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Thu, 06 Mar 2025 12:22:45 +01:00

uprobes/x86: Harden uretprobe syscall trampoline check

Jann reported a possible issue when trampoline_check_ip returns
address near the bottom of the address space that is allowed to
call into the syscall if uretprobes are not set up:

   https://lore.kernel.org/bpf/202502081235.5A6F352985@keescook/T/#m9d416df341b8fbc11737dacbcd29f0054413cbbf

Though the mmap minimum address restrictions will typically prevent
creating mappings there, let's make sure uretprobe syscall checks
for that.

Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
Reported-by: Jann Horn <jannh@...gle.com>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Oleg Nesterov <oleg@...hat.com>
Reviewed-by: Kees Cook <kees@...nel.org>
Acked-by: Andrii Nakryiko <andrii@...nel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Acked-by: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20250212220433.3624297-1-jolsa@kernel.org
---
 arch/x86/kernel/uprobes.c | 14 +++++++++-----
 include/linux/uprobes.h   |  2 ++
 kernel/events/uprobes.c   |  2 +-
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 5a952c5..9194695 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -357,19 +357,23 @@ void *arch_uprobe_trampoline(unsigned long *psize)
 	return &insn;
 }
 
-static unsigned long trampoline_check_ip(void)
+static unsigned long trampoline_check_ip(unsigned long tramp)
 {
-	unsigned long tramp = uprobe_get_trampoline_vaddr();
-
 	return tramp + (uretprobe_syscall_check - uretprobe_trampoline_entry);
 }
 
 SYSCALL_DEFINE0(uretprobe)
 {
 	struct pt_regs *regs = task_pt_regs(current);
-	unsigned long err, ip, sp, r11_cx_ax[3];
+	unsigned long err, ip, sp, r11_cx_ax[3], tramp;
+
+	/* If there's no trampoline, we are called from wrong place. */
+	tramp = uprobe_get_trampoline_vaddr();
+	if (unlikely(tramp == UPROBE_NO_TRAMPOLINE_VADDR))
+		goto sigill;
 
-	if (regs->ip != trampoline_check_ip())
+	/* Make sure the ip matches the only allowed sys_uretprobe caller. */
+	if (unlikely(regs->ip != trampoline_check_ip(tramp)))
 		goto sigill;
 
 	err = copy_from_user(r11_cx_ax, (void __user *)regs->sp, sizeof(r11_cx_ax));
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index a40efdd..2e46b69 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -39,6 +39,8 @@ struct page;
 
 #define MAX_URETPROBE_DEPTH		64
 
+#define UPROBE_NO_TRAMPOLINE_VADDR	(~0UL)
+
 struct uprobe_consumer {
 	/*
 	 * handler() can return UPROBE_HANDLER_REMOVE to signal the need to
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 921ad91..70c84b9 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -2169,8 +2169,8 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
  */
 unsigned long uprobe_get_trampoline_vaddr(void)
 {
+	unsigned long trampoline_vaddr = UPROBE_NO_TRAMPOLINE_VADDR;
 	struct xol_area *area;
-	unsigned long trampoline_vaddr = -1;
 
 	/* Pairs with xol_add_vma() smp_store_release() */
 	area = READ_ONCE(current->mm->uprobes_state.xol_area); /* ^^^ */