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/xtensa/lib/memset.S | 155 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 155 insertions(+) create mode 100644 arch/xtensa/lib/memset.S (limited to 'arch/xtensa/lib/memset.S') diff --git a/arch/xtensa/lib/memset.S b/arch/xtensa/lib/memset.S new file mode 100644 index 000000000..262c3f39f --- /dev/null +++ b/arch/xtensa/lib/memset.S @@ -0,0 +1,155 @@ +/* + * arch/xtensa/lib/memset.S + * + * ANSI C standard library function memset + * (Well, almost. .fixup code might return zero.) + * + * This file is subject to the terms and conditions of the GNU General + * Public License. See the file "COPYING" in the main directory of + * this archive for more details. + * + * Copyright (C) 2002 Tensilica Inc. + */ + +#include +#include +#include + +/* + * void *memset(void *dst, int c, size_t length) + * + * The algorithm is as follows: + * Create a word with c in all byte positions + * If the destination is aligned, + * do 16B chucks with a loop, and then finish up with + * 8B, 4B, 2B, and 1B stores conditional on the length. + * If destination is unaligned, align it by conditionally + * setting 1B and 2B and then go to aligned case. + * This code tries to use fall-through branches for the common + * case of an aligned destination (except for the branches to + * the alignment labels). + */ + +.text +ENTRY(__memset) +WEAK(memset) + + abi_entry_default + # a2/ dst, a3/ c, a4/ length + extui a3, a3, 0, 8 # mask to just 8 bits + slli a7, a3, 8 # duplicate character in all bytes of word + or a3, a3, a7 # ... + slli a7, a3, 16 # ... + or a3, a3, a7 # ... + mov a5, a2 # copy dst so that a2 is return value + movi a6, 3 # for alignment tests + bany a2, a6, .Ldstunaligned # if dst is unaligned +.L0: # return here from .Ldstunaligned when dst is aligned + srli a7, a4, 4 # number of loop iterations with 16B + # per iteration + bnez a4, .Laligned + abi_ret_default + +/* + * Destination is word-aligned. + */ + # set 16 bytes per iteration for word-aligned dst + .align 4 # 1 mod 4 alignment for LOOPNEZ + .byte 0 # (0 mod 4 alignment for LBEG) +.Laligned: +#if XCHAL_HAVE_LOOPS + loopnez a7, .Loop1done +#else /* !XCHAL_HAVE_LOOPS */ + beqz a7, .Loop1done + slli a6, a7, 4 + add a6, a6, a5 # a6 = end of last 16B chunk +#endif /* !XCHAL_HAVE_LOOPS */ +.Loop1: +EX(10f) s32i a3, a5, 0 +EX(10f) s32i a3, a5, 4 +EX(10f) s32i a3, a5, 8 +EX(10f) s32i a3, a5, 12 + addi a5, a5, 16 +#if !XCHAL_HAVE_LOOPS + blt a5, a6, .Loop1 +#endif /* !XCHAL_HAVE_LOOPS */ +.Loop1done: + bbci.l a4, 3, .L2 + # set 8 bytes +EX(10f) s32i a3, a5, 0 +EX(10f) s32i a3, a5, 4 + addi a5, a5, 8 +.L2: + bbci.l a4, 2, .L3 + # set 4 bytes +EX(10f) s32i a3, a5, 0 + addi a5, a5, 4 +.L3: + bbci.l a4, 1, .L4 + # set 2 bytes +EX(10f) s16i a3, a5, 0 + addi a5, a5, 2 +.L4: + bbci.l a4, 0, .L5 + # set 1 byte +EX(10f) s8i a3, a5, 0 +.L5: +.Lret1: + abi_ret_default + +/* + * Destination is unaligned + */ + +.Ldstunaligned: + bltui a4, 8, .Lbyteset # do short copies byte by byte + bbci.l a5, 0, .L20 # branch if dst alignment half-aligned + # dst is only byte aligned + # set 1 byte +EX(10f) s8i a3, a5, 0 + addi a5, a5, 1 + addi a4, a4, -1 + # now retest if dst aligned + bbci.l a5, 1, .L0 # if now aligned, return to main algorithm +.L20: + # dst half-aligned + # set 2 bytes +EX(10f) s16i a3, a5, 0 + addi a5, a5, 2 + addi a4, a4, -2 + j .L0 # dst is now aligned, return to main algorithm + +/* + * Byte by byte set + */ + .align 4 + .byte 0 # 1 mod 4 alignment for LOOPNEZ + # (0 mod 4 alignment for LBEG) +.Lbyteset: +#if XCHAL_HAVE_LOOPS + loopnez a4, .Lbytesetdone +#else /* !XCHAL_HAVE_LOOPS */ + beqz a4, .Lbytesetdone + add a6, a5, a4 # a6 = ending address +#endif /* !XCHAL_HAVE_LOOPS */ +.Lbyteloop: +EX(10f) s8i a3, a5, 0 + addi a5, a5, 1 +#if !XCHAL_HAVE_LOOPS + blt a5, a6, .Lbyteloop +#endif /* !XCHAL_HAVE_LOOPS */ +.Lbytesetdone: + abi_ret_default + +ENDPROC(__memset) +EXPORT_SYMBOL(__memset) +EXPORT_SYMBOL(memset) + + .section .fixup, "ax" + .align 4 + +/* We return zero if a failure occurred. */ + +10: + movi a2, 0 + abi_ret_default -- cgit v1.3.1