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SubjectRe: [RFC PATCH 1/2] x86/kprobes: Prohibit kprobing on INT and UD
From
On 1/26/2024 8:41 PM, Jinghao Jia wrote:
> Both INTs (INT n, INT1, INT3, INTO) and UDs (UD0, UD1, UD2) serve
> special purposes in the kernel, e.g., INT3 is used by KGDB and UD2 is
> involved in LLVM-KCFI instrumentation. At the same time, attaching
> kprobes on these instructions (particularly UDs) will pollute the stack
> trace dumped in the kernel ring buffer, since the exception is triggered
> in the copy buffer rather than the original location.
>
> Check for INTs and UDs in can_probe and reject any kprobes trying to
> attach to these instructions.
>
> Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Signed-off-by: Jinghao Jia <jinghao7@illinois.edu>
> ---
> arch/x86/kernel/kprobes/core.c | 33 ++++++++++++++++++++++++++-------
> 1 file changed, 26 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index e8babebad7b8..792b38d22126 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -252,6 +252,22 @@ unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long add
> return __recover_probed_insn(buf, addr);
> }
>
> +static inline int is_exception_insn(struct insn *insn)

s/int/bool

> +{
> + if (insn->opcode.bytes[0] == 0x0f) {
> + /* UD0 / UD1 / UD2 */
> + return insn->opcode.bytes[1] == 0xff ||
> + insn->opcode.bytes[1] == 0xb9 ||
> + insn->opcode.bytes[1] == 0x0b;
> + } else {
> + /* INT3 / INT n / INTO / INT1 */
> + return insn->opcode.bytes[0] == 0xcc ||
> + insn->opcode.bytes[0] == 0xcd ||
> + insn->opcode.bytes[0] == 0xce ||
> + insn->opcode.bytes[0] == 0xf1;
> + }
> +}
> +
> /* Check if paddr is at an instruction boundary */
> static int can_probe(unsigned long paddr)
> {
> @@ -294,6 +310,16 @@ static int can_probe(unsigned long paddr)
> #endif
> addr += insn.length;
> }
> + __addr = recover_probed_instruction(buf, addr);
> + if (!__addr)
> + return 0;
> +
> + if (insn_decode_kernel(&insn, (void *)__addr) < 0)
> + return 0;
> +
> + if (is_exception_insn(&insn))
> + return 0;
> +
> if (IS_ENABLED(CONFIG_CFI_CLANG)) {
> /*
> * The compiler generates the following instruction sequence
> @@ -308,13 +334,6 @@ static int can_probe(unsigned long paddr)
> * Also, these movl and addl are used for showing expected
> * type. So those must not be touched.
> */
> - __addr = recover_probed_instruction(buf, addr);
> - if (!__addr)
> - return 0;
> -
> - if (insn_decode_kernel(&insn, (void *)__addr) < 0)
> - return 0;
> -
> if (insn.opcode.value == 0xBA)
> offset = 12;
> else if (insn.opcode.value == 0x3)

--
Thanks!
Xin


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