From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions When using eBPF to probe CS CALL instructions within a function, a crash can be triggered. The eBPF tool probes offset 257 of the __hrtimer_run_queues() function: <__hrtimer_run_queues+249>: nopl 0x0(%rax,%rax,1) <__hrtimer_run_queues+254>: mov %r14,%rdi <__hrtimer_run_queues+257>: cs call <__x86_indirect_thunk_r12> <__hrtimer_run_queues+263>: mov %eax,%r12d <__hrtimer_run_queues+266>: xchg %ax,%ax <__hrtimer_run_queues+268>: mov %r13,%rdi Which triggers this crash: BUG: unable to handle page fault for address: 00000000000f41c9 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P RIP: 0010:__hrtimer_run_queues+0x106/0x230 Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is at the 6th byte of the above CS CALL instruction. Since the CS CALL instruction occupies 6 bytes, the exception occurred in the middle of that call instruction. The root cause is that when using eBPF tools to probe in the middle of a function, a kprobe with INT3 is used as the underlying implementation. During single-step emulation of the original CALL instruction, int3_emulate_call() assumes that the probed CALL instruction is 5 bytes long. However, the actual CS-prefixed CALL instruction occupies 6 bytes, so it constructs an incorrect exception return address. When the CPU returns from the kprobe handler, the next instruction to be executed is at the address of the last byte of that CS CALL instruction. Coincidentally, starting from that address, the CPU fetches and decodes a completely different instruction, which ultimately triggers a kernel crash. Fix the issue by using the actual instruction length obtained from the instruction decoder when constructing the exception return address, rather than relying on the hardcoded CALL_INSN_SIZE macro. [ mingo: Refined the changelog ] Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- arch/microblaze/lib/divsi3.S | 74 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 74 insertions(+) create mode 100644 arch/microblaze/lib/divsi3.S (limited to 'arch/microblaze/lib/divsi3.S') diff --git a/arch/microblaze/lib/divsi3.S b/arch/microblaze/lib/divsi3.S new file mode 100644 index 000000000..919fb69f8 --- /dev/null +++ b/arch/microblaze/lib/divsi3.S @@ -0,0 +1,74 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#include + +/* +* Divide operation for 32 bit integers. +* Input : Dividend in Reg r5 +* Divisor in Reg r6 +* Output: Result in Reg r3 +*/ + .text + .globl __divsi3 + .type __divsi3, @function + .ent __divsi3 +__divsi3: + .frame r1, 0, r15 + + addik r1, r1, -16 + swi r28, r1, 0 + swi r29, r1, 4 + swi r30, r1, 8 + swi r31, r1, 12 + + beqi r6, div_by_zero /* div_by_zero - division error */ + beqi r5, result_is_zero /* result is zero */ + bgeid r5, r5_pos + xor r28, r5, r6 /* get the sign of the result */ + rsubi r5, r5, 0 /* make r5 positive */ +r5_pos: + bgei r6, r6_pos + rsubi r6, r6, 0 /* make r6 positive */ +r6_pos: + addik r30, r0, 0 /* clear mod */ + addik r3, r0, 0 /* clear div */ + addik r29, r0, 32 /* initialize the loop count */ + + /* first part try to find the first '1' in the r5 */ +div0: + blti r5, div2 /* this traps r5 == 0x80000000 */ +div1: + add r5, r5, r5 /* left shift logical r5 */ + bgtid r5, div1 + addik r29, r29, -1 +div2: + /* left shift logical r5 get the '1' into the carry */ + add r5, r5, r5 + addc r30, r30, r30 /* move that bit into the mod register */ + rsub r31, r6, r30 /* try to subtract (r30 a r6) */ + blti r31, mod_too_small + /* move the r31 to mod since the result was positive */ + or r30, r0, r31 + addik r3, r3, 1 +mod_too_small: + addik r29, r29, -1 + beqi r29, loop_end + add r3, r3, r3 /* shift in the '1' into div */ + bri div2 /* div2 */ +loop_end: + bgei r28, return_here + brid return_here + rsubi r3, r3, 0 /* negate the result */ +div_by_zero: +result_is_zero: + or r3, r0, r0 /* set result to 0 */ +return_here: +/* restore values of csrs and that of r3 and the divisor and the dividend */ + lwi r28, r1, 0 + lwi r29, r1, 4 + lwi r30, r1, 8 + lwi r31, r1, 12 + rtsd r15, 8 + addik r1, r1, 16 + +.size __divsi3, . - __divsi3 +.end __divsi3 -- cgit v1.3.1