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/arc/lib/memcpy-archs.S | 219 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 219 insertions(+) create mode 100644 arch/arc/lib/memcpy-archs.S (limited to 'arch/arc/lib/memcpy-archs.S') diff --git a/arch/arc/lib/memcpy-archs.S b/arch/arc/lib/memcpy-archs.S new file mode 100644 index 000000000..0051a84f6 --- /dev/null +++ b/arch/arc/lib/memcpy-archs.S @@ -0,0 +1,219 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2014-15 Synopsys, Inc. (www.synopsys.com) + */ + +#include + +#ifdef __LITTLE_ENDIAN__ +# define SHIFT_1(RX,RY,IMM) asl RX, RY, IMM ; << +# define SHIFT_2(RX,RY,IMM) lsr RX, RY, IMM ; >> +# define MERGE_1(RX,RY,IMM) asl RX, RY, IMM +# define MERGE_2(RX,RY,IMM) +# define EXTRACT_1(RX,RY,IMM) and RX, RY, 0xFFFF +# define EXTRACT_2(RX,RY,IMM) lsr RX, RY, IMM +#else +# define SHIFT_1(RX,RY,IMM) lsr RX, RY, IMM ; >> +# define SHIFT_2(RX,RY,IMM) asl RX, RY, IMM ; << +# define MERGE_1(RX,RY,IMM) asl RX, RY, IMM ; << +# define MERGE_2(RX,RY,IMM) asl RX, RY, IMM ; << +# define EXTRACT_1(RX,RY,IMM) lsr RX, RY, IMM +# define EXTRACT_2(RX,RY,IMM) lsr RX, RY, 0x08 +#endif + +#ifdef CONFIG_ARC_HAS_LL64 +# define LOADX(DST,RX) ldd.ab DST, [RX, 8] +# define STOREX(SRC,RX) std.ab SRC, [RX, 8] +# define ZOLSHFT 5 +# define ZOLAND 0x1F +#else +# define LOADX(DST,RX) ld.ab DST, [RX, 4] +# define STOREX(SRC,RX) st.ab SRC, [RX, 4] +# define ZOLSHFT 4 +# define ZOLAND 0xF +#endif + +ENTRY_CFI(memcpy) + mov.f 0, r2 +;;; if size is zero + jz.d [blink] + mov r3, r0 ; don;t clobber ret val + +;;; if size <= 8 + cmp r2, 8 + bls.d @.Lsmallchunk + mov.f lp_count, r2 + + and.f r4, r0, 0x03 + rsub lp_count, r4, 4 + lpnz @.Laligndestination + ;; LOOP BEGIN + ldb.ab r5, [r1,1] + sub r2, r2, 1 + stb.ab r5, [r3,1] +.Laligndestination: + +;;; Check the alignment of the source + and.f r4, r1, 0x03 + bnz.d @.Lsourceunaligned + +;;; CASE 0: Both source and destination are 32bit aligned +;;; Convert len to Dwords, unfold x4 + lsr.f lp_count, r2, ZOLSHFT + lpnz @.Lcopy32_64bytes + ;; LOOP START + LOADX (r6, r1) + LOADX (r8, r1) + LOADX (r10, r1) + LOADX (r4, r1) + STOREX (r6, r3) + STOREX (r8, r3) + STOREX (r10, r3) + STOREX (r4, r3) +.Lcopy32_64bytes: + + and.f lp_count, r2, ZOLAND ;Last remaining 31 bytes +.Lsmallchunk: + lpnz @.Lcopyremainingbytes + ;; LOOP START + ldb.ab r5, [r1,1] + stb.ab r5, [r3,1] +.Lcopyremainingbytes: + + j [blink] +;;; END CASE 0 + +.Lsourceunaligned: + cmp r4, 2 + beq.d @.LunalignedOffby2 + sub r2, r2, 1 + + bhi.d @.LunalignedOffby3 + ldb.ab r5, [r1, 1] + +;;; CASE 1: The source is unaligned, off by 1 + ;; Hence I need to read 1 byte for a 16bit alignment + ;; and 2bytes to reach 32bit alignment + ldh.ab r6, [r1, 2] + sub r2, r2, 2 + ;; Convert to words, unfold x2 + lsr.f lp_count, r2, 3 + MERGE_1 (r6, r6, 8) + MERGE_2 (r5, r5, 24) + or r5, r5, r6 + + ;; Both src and dst are aligned + lpnz @.Lcopy8bytes_1 + ;; LOOP START + ld.ab r6, [r1, 4] + ld.ab r8, [r1,4] + + SHIFT_1 (r7, r6, 24) + or r7, r7, r5 + SHIFT_2 (r5, r6, 8) + + SHIFT_1 (r9, r8, 24) + or r9, r9, r5 + SHIFT_2 (r5, r8, 8) + + st.ab r7, [r3, 4] + st.ab r9, [r3, 4] +.Lcopy8bytes_1: + + ;; Write back the remaining 16bits + EXTRACT_1 (r6, r5, 16) + sth.ab r6, [r3, 2] + ;; Write back the remaining 8bits + EXTRACT_2 (r5, r5, 16) + stb.ab r5, [r3, 1] + + and.f lp_count, r2, 0x07 ;Last 8bytes + lpnz @.Lcopybytewise_1 + ;; LOOP START + ldb.ab r6, [r1,1] + stb.ab r6, [r3,1] +.Lcopybytewise_1: + j [blink] + +.LunalignedOffby2: +;;; CASE 2: The source is unaligned, off by 2 + ldh.ab r5, [r1, 2] + sub r2, r2, 1 + + ;; Both src and dst are aligned + ;; Convert to words, unfold x2 + lsr.f lp_count, r2, 3 +#ifdef __BIG_ENDIAN__ + asl.nz r5, r5, 16 +#endif + lpnz @.Lcopy8bytes_2 + ;; LOOP START + ld.ab r6, [r1, 4] + ld.ab r8, [r1,4] + + SHIFT_1 (r7, r6, 16) + or r7, r7, r5 + SHIFT_2 (r5, r6, 16) + + SHIFT_1 (r9, r8, 16) + or r9, r9, r5 + SHIFT_2 (r5, r8, 16) + + st.ab r7, [r3, 4] + st.ab r9, [r3, 4] +.Lcopy8bytes_2: + +#ifdef __BIG_ENDIAN__ + lsr.nz r5, r5, 16 +#endif + sth.ab r5, [r3, 2] + + and.f lp_count, r2, 0x07 ;Last 8bytes + lpnz @.Lcopybytewise_2 + ;; LOOP START + ldb.ab r6, [r1,1] + stb.ab r6, [r3,1] +.Lcopybytewise_2: + j [blink] + +.LunalignedOffby3: +;;; CASE 3: The source is unaligned, off by 3 +;;; Hence, I need to read 1byte for achieve the 32bit alignment + + ;; Both src and dst are aligned + ;; Convert to words, unfold x2 + lsr.f lp_count, r2, 3 +#ifdef __BIG_ENDIAN__ + asl.ne r5, r5, 24 +#endif + lpnz @.Lcopy8bytes_3 + ;; LOOP START + ld.ab r6, [r1, 4] + ld.ab r8, [r1,4] + + SHIFT_1 (r7, r6, 8) + or r7, r7, r5 + SHIFT_2 (r5, r6, 24) + + SHIFT_1 (r9, r8, 8) + or r9, r9, r5 + SHIFT_2 (r5, r8, 24) + + st.ab r7, [r3, 4] + st.ab r9, [r3, 4] +.Lcopy8bytes_3: + +#ifdef __BIG_ENDIAN__ + lsr.nz r5, r5, 24 +#endif + stb.ab r5, [r3, 1] + + and.f lp_count, r2, 0x07 ;Last 8bytes + lpnz @.Lcopybytewise_3 + ;; LOOP START + ldb.ab r6, [r1,1] + stb.ab r6, [r3,1] +.Lcopybytewise_3: + j [blink] + +END_CFI(memcpy) -- cgit v1.3.1