[tip: x86/urgent] kprobes/x86: Use copy_from_kernel_nofault() to read from unsafe address

[tip-bot2 for Masami Hiramatsu (Google)]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     4e51653d5d871f40f1bd5cf95cc7f2d8b33d063b
Gitweb:        https://git.kernel.org/tip/4e51653d5d871f40f1bd5cf95cc7f2d8b33d063b
Author:        Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
AuthorDate:    Fri, 15 Mar 2024 00:17:30 +09:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 22 Mar 2024 11:40:56 +01:00

kprobes/x86: Use copy_from_kernel_nofault() to read from unsafe address

Read from an unsafe address with copy_from_kernel_nofault() in
arch_adjust_kprobe_addr() because this function is used before checking
the address is in text or not. Syzcaller bot found a bug and reported
the case if user specifies inaccessible data area,
arch_adjust_kprobe_addr() will cause a kernel panic.

[ mingo: Clarified the comment. ]

Fixes: cc66bb914578 ("x86/ibt,kprobes: Cure sym+0 equals fentry woes")
Reported-by: Qiang Zhang <zzqq0103.hey@xxxxxxxxx>
Tested-by: Jinghao Jia <jinghao7@xxxxxxxxxxxx>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/171042945004.154897.2221804961882915806.stgit@devnote2
---
 arch/x86/kernel/kprobes/core.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 091b3ab..d0e49bd 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -373,7 +373,16 @@ out:
 kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
 					 bool *on_func_entry)
 {
-	if (is_endbr(*(u32 *)addr)) {
+	u32 insn;
+
+	/*
+	 * Since 'addr' is not guaranteed to be safe to access, use
+	 * copy_from_kernel_nofault() to read the instruction:
+	 */
+	if (copy_from_kernel_nofault(&insn, (void *)addr, sizeof(u32)))
+		return NULL;
+
+	if (is_endbr(insn)) {
 		*on_func_entry = !offset || offset == 4;
 		if (*on_func_entry)
 			offset = 4;