2019-09-03 11:09:38

by Masami Hiramatsu

Subject: [PATCH -tip v2] kprobes: Prohibit probing on BUG() and WARN() address

Since BUG() and WARN() may use a trap (e.g. UD2 on x86) to
get the address where the BUG() has occurred, kprobes can not
do single-step out-of-line that instruction. So prohibit
probing on such address.

Without this fix, if someone put a kprobe on WARN(), the
kernel will crash with invalid opcode error instead of
outputing warning message, because kernel can not find
correct bug address.

Signed-off-by: Masami Hiramatsu <[email protected]>
---
Changes in v2:
- Add find_bug() stub function for !CONFIG_GENERIC_BUG
- Cast the p->addr to unsigned long.
---
include/linux/bug.h | 5 +++++
kernel/kprobes.c | 3 ++-
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/bug.h b/include/linux/bug.h
index fe5916550da8..f639bd0122f3 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -47,6 +47,11 @@ void generic_bug_clear_once(void);

#else /* !CONFIG_GENERIC_BUG */

+static inline void *find_bug(unsigned long bugaddr)
+{
+ return NULL;
+}
+
static inline enum bug_trap_type report_bug(unsigned long bug_addr,
struct pt_regs *regs)
{
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 452151e79535..5bdf47190f09 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1514,7 +1514,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
/* Ensure it is not in reserved area nor out of text */
if (!kernel_text_address((unsigned long) p->addr) ||
within_kprobe_blacklist((unsigned long) p->addr) ||
- jump_label_text_reserved(p->addr, p->addr)) {
+ jump_label_text_reserved(p->addr, p->addr) ||
+ find_bug((unsigned long) p->addr)) {
ret = -EINVAL;
goto out;
}

2019-09-04 09:14:45

by Naveen N. Rao

Subject: Re: [PATCH -tip v2] kprobes: Prohibit probing on BUG() and WARN() address

Masami Hiramatsu wrote:
> Since BUG() and WARN() may use a trap (e.g. UD2 on x86) to
> get the address where the BUG() has occurred, kprobes can not
> do single-step out-of-line that instruction. So prohibit
> probing on such address.
>
> Without this fix, if someone put a kprobe on WARN(), the
> kernel will crash with invalid opcode error instead of
> outputing warning message, because kernel can not find
> correct bug address.
>
> Signed-off-by: Masami Hiramatsu <[email protected]>
> ---
> Changes in v2:
> - Add find_bug() stub function for !CONFIG_GENERIC_BUG
> - Cast the p->addr to unsigned long.
> ---
> include/linux/bug.h | 5 +++++
> kernel/kprobes.c | 3 ++-
> 2 files changed, 7 insertions(+), 1 deletion(-)

Acked-by: Naveen N. Rao <[email protected]>

- Naveen

2019-09-04 12:30:24

by Steven Rostedt

Subject: Re: [PATCH -tip v2] kprobes: Prohibit probing on BUG() and WARN() address

On Tue, 3 Sep 2019 20:08:21 +0900
Masami Hiramatsu <[email protected]> wrote:

> Since BUG() and WARN() may use a trap (e.g. UD2 on x86) to
> get the address where the BUG() has occurred, kprobes can not
> do single-step out-of-line that instruction. So prohibit
> probing on such address.
>
> Without this fix, if someone put a kprobe on WARN(), the
> kernel will crash with invalid opcode error instead of
> outputing warning message, because kernel can not find
> correct bug address.
>
> Signed-off-by: Masami Hiramatsu <[email protected]>

Acked-by: Steven Rostedt (VMware) <[email protected]>

-- Steve

> ---
> Changes in v2:
> - Add find_bug() stub function for !CONFIG_GENERIC_BUG
> - Cast the p->addr to unsigned long.
> ---
> include/linux/bug.h | 5 +++++
> kernel/kprobes.c | 3 ++-
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bug.h b/include/linux/bug.h
> index fe5916550da8..f639bd0122f3 100644
> --- a/include/linux/bug.h
> +++ b/include/linux/bug.h
> @@ -47,6 +47,11 @@ void generic_bug_clear_once(void);
>
> #else /* !CONFIG_GENERIC_BUG */
>
> +static inline void *find_bug(unsigned long bugaddr)
> +{
> + return NULL;
> +}
> +
> static inline enum bug_trap_type report_bug(unsigned long bug_addr,
> struct pt_regs *regs)
> {
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 452151e79535..5bdf47190f09 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1514,7 +1514,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
> /* Ensure it is not in reserved area nor out of text */
> if (!kernel_text_address((unsigned long) p->addr) ||
> within_kprobe_blacklist((unsigned long) p->addr) ||
> - jump_label_text_reserved(p->addr, p->addr)) {
> + jump_label_text_reserved(p->addr, p->addr) ||
> + find_bug((unsigned long) p->addr)) {
> ret = -EINVAL;
> goto out;
> }