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 --- Documentation/ABI/testing/sysfs-fs-ext4 | 118 ++++++++++++++++++++++++++++++++ 1 file changed, 118 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-fs-ext4 (limited to 'Documentation/ABI/testing/sysfs-fs-ext4') diff --git a/Documentation/ABI/testing/sysfs-fs-ext4 b/Documentation/ABI/testing/sysfs-fs-ext4 new file mode 100644 index 000000000..2edd0a667 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-fs-ext4 @@ -0,0 +1,118 @@ +What: /sys/fs/ext4//mb_stats +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + Controls whether the multiblock allocator should + collect statistics, which are shown during the unmount. + 1 means to collect statistics, 0 means not to collect + statistics + +What: /sys/fs/ext4//mb_group_prealloc +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + The multiblock allocator will round up allocation + requests to a multiple of this tuning parameter if the + stripe size is not set in the ext4 superblock + +What: /sys/fs/ext4//mb_max_to_scan +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + The maximum number of extents the multiblock allocator + will search to find the best extent + +What: /sys/fs/ext4//mb_min_to_scan +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + The minimum number of extents the multiblock allocator + will search to find the best extent + +What: /sys/fs/ext4//mb_order2_req +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + Tuning parameter which controls the minimum size for + requests (as a power of 2) where the buddy cache is + used + +What: /sys/fs/ext4//mb_stream_req +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + Files which have fewer blocks than this tunable + parameter will have their blocks allocated out of a + block group specific preallocation pool, so that small + files are packed closely together. Each large file + will have its blocks allocated out of its own unique + preallocation pool. + +What: /sys/fs/ext4//inode_readahead_blks +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + Tuning parameter which controls the maximum number of + inode table blocks that ext4's inode table readahead + algorithm will pre-read into the buffer cache + +What: /sys/fs/ext4//delayed_allocation_blocks +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + This file is read-only and shows the number of blocks + that are dirty in the page cache, but which do not + have their location in the filesystem allocated yet. + +What: /sys/fs/ext4//lifetime_write_kbytes +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + This file is read-only and shows the number of kilobytes + of data that have been written to this filesystem since it was + created. + +What: /sys/fs/ext4//session_write_kbytes +Date: March 2008 +Contact: "Theodore Ts'o" +Description: + This file is read-only and shows the number of + kilobytes of data that have been written to this + filesystem since it was mounted. + +What: /sys/fs/ext4//inode_goal +Date: June 2008 +Contact: "Theodore Ts'o" +Description: + Tuning parameter which (if non-zero) controls the goal + inode used by the inode allocator in preference to + all other allocation heuristics. This is intended for + debugging use only, and should be 0 on production + systems. + +What: /sys/fs/ext4//max_writeback_mb_bump +Date: September 2009 +Contact: "Theodore Ts'o" +Description: + The maximum number of megabytes the writeback code will + try to write out before move on to another inode. + +What: /sys/fs/ext4//extent_max_zeroout_kb +Date: August 2012 +Contact: "Theodore Ts'o" +Description: + The maximum number of kilobytes which will be zeroed + out in preference to creating a new uninitialized + extent when manipulating an inode's extent tree. Note + that using a larger value will increase the + variability of time necessary to complete a random + write operation (since a 4k random write might turn + into a much larger write due to the zeroout + operation). + +What: /sys/fs/ext4//journal_task +Date: February 2019 +Contact: "Theodore Ts'o" +Description: + This file is read-only and shows the pid of journal thread in + current pid-namespace or 0 if task is unreachable. -- cgit v1.3.1