[PATCH v2 1/2] kprobes: Prohibit probing on CFI preamble symbol

From: Masami Hiramatsu (Google)
Date: Mon Jul 10 2023 - 21:51:30 EST


From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Do not allow to probe on "__cfi_" or "__pfx_" started symbol, because those
are used for CFI and not executed. Probing it will break the CFI.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
Changes in v2:
- Check "__pfx_" prefix functions too.
- Make the check unconditional.
---
kernel/kprobes.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 00e177de91cc..3da9726232ff 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1545,6 +1545,17 @@ static int check_ftrace_location(struct kprobe *p)
return 0;
}

+static bool is_cfi_preamble_symbol(unsigned long addr)
+{
+ char symbuf[KSYM_NAME_LEN];
+
+ if (lookup_symbol_name(addr, symbuf))
+ return false;
+
+ return str_has_prefix("__cfi_", symbuf) ||
+ str_has_prefix("__pfx_", symbuf);
+}
+
static int check_kprobe_address_safe(struct kprobe *p,
struct module **probed_mod)
{
@@ -1563,7 +1574,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
within_kprobe_blacklist((unsigned long) p->addr) ||
jump_label_text_reserved(p->addr, p->addr) ||
static_call_text_reserved(p->addr, p->addr) ||
- find_bug((unsigned long)p->addr)) {
+ find_bug((unsigned long)p->addr) ||
+ is_cfi_preamble_symbol((unsigned long)p->addr)) {
ret = -EINVAL;
goto out;
}