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/openrisc/lib/string.S | 101 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 101 insertions(+) create mode 100644 arch/openrisc/lib/string.S (limited to 'arch/openrisc/lib/string.S') diff --git a/arch/openrisc/lib/string.S b/arch/openrisc/lib/string.S new file mode 100644 index 000000000..74046f2eb --- /dev/null +++ b/arch/openrisc/lib/string.S @@ -0,0 +1,101 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * OpenRISC string.S + * + * Linux architectural port borrowing liberally from similar works of + * others. All original copyrights apply as per the original source + * declaration. + * + * Modifications for the OpenRISC architecture: + * Copyright (C) 2003 Matjaz Breskvar + * Copyright (C) 2010-2011 Jonas Bonn + */ + +#include +#include + + /* + * this can be optimized by doing gcc inline assemlby with + * proper constraints (no need to save args registers...) + * + */ + + +/* + * + * int __copy_tofrom_user(void *to, const void *from, unsigned long size); + * + * NOTE: it returns number of bytes NOT copied !!! + * + */ + .global __copy_tofrom_user +__copy_tofrom_user: + l.addi r1,r1,-12 + l.sw 0(r1),r6 + l.sw 4(r1),r4 + l.sw 8(r1),r3 + + l.addi r11,r5,0 +2: l.sfeq r11,r0 + l.bf 1f + l.addi r11,r11,-1 +8: l.lbz r6,0(r4) +9: l.sb 0(r3),r6 + l.addi r3,r3,1 + l.j 2b + l.addi r4,r4,1 +1: + l.addi r11,r11,1 // r11 holds the return value + + l.lwz r6,0(r1) + l.lwz r4,4(r1) + l.lwz r3,8(r1) + l.jr r9 + l.addi r1,r1,12 + + .section .fixup, "ax" +99: + l.j 1b + l.nop + .previous + + .section __ex_table, "a" + .long 8b, 99b // read fault + .long 9b, 99b // write fault + .previous + +/* + * unsigned long clear_user(void *addr, unsigned long size) ; + * + * NOTE: it returns number of bytes NOT cleared !!! + */ + .global __clear_user +__clear_user: + l.addi r1,r1,-8 + l.sw 0(r1),r4 + l.sw 4(r1),r3 + +2: l.sfeq r4,r0 + l.bf 1f + l.addi r4,r4,-1 +9: l.sb 0(r3),r0 + l.j 2b + l.addi r3,r3,1 + +1: + l.addi r11,r4,1 + + l.lwz r4,0(r1) + l.lwz r3,4(r1) + l.jr r9 + l.addi r1,r1,8 + + .section .fixup, "ax" +99: + l.j 1b + l.nop + .previous + + .section __ex_table, "a" + .long 9b, 99b // write fault + .previous -- cgit v1.3.1