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 --- fs/xfs/scrub/rtbitmap.c | 299 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 299 insertions(+) create mode 100644 fs/xfs/scrub/rtbitmap.c (limited to 'fs/xfs/scrub/rtbitmap.c') diff --git a/fs/xfs/scrub/rtbitmap.c b/fs/xfs/scrub/rtbitmap.c new file mode 100644 index 000000000..52c24d3d4 --- /dev/null +++ b/fs/xfs/scrub/rtbitmap.c @@ -0,0 +1,299 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) 2017-2023 Oracle. All Rights Reserved. + * Author: Darrick J. Wong + */ +#include "xfs_platform.h" +#include "xfs_fs.h" +#include "xfs_shared.h" +#include "xfs_format.h" +#include "xfs_trans_resv.h" +#include "xfs_mount.h" +#include "xfs_btree.h" +#include "xfs_log_format.h" +#include "xfs_trans.h" +#include "xfs_rtbitmap.h" +#include "xfs_inode.h" +#include "xfs_bmap.h" +#include "xfs_bit.h" +#include "xfs_rtgroup.h" +#include "xfs_sb.h" +#include "xfs_rmap.h" +#include "xfs_rtrmap_btree.h" +#include "xfs_exchmaps.h" +#include "xfs_zone_alloc.h" +#include "scrub/scrub.h" +#include "scrub/common.h" +#include "scrub/repair.h" +#include "scrub/tempexch.h" +#include "scrub/rtbitmap.h" +#include "scrub/btree.h" + +/* Set us up with the realtime metadata locked. */ +int +xchk_setup_rtbitmap( + struct xfs_scrub *sc) +{ + struct xfs_mount *mp = sc->mp; + struct xchk_rtbitmap *rtb; + int error; + + if (xchk_need_intent_drain(sc)) + xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN); + + rtb = kzalloc_flex(*rtb, words, xchk_rtbitmap_wordcnt(sc), + XCHK_GFP_FLAGS); + if (!rtb) + return -ENOMEM; + sc->buf = rtb; + rtb->sc = sc; + + error = xchk_rtgroup_init(sc, sc->sm->sm_agno, &sc->sr); + if (error) + return error; + + if (xchk_could_repair(sc)) { + error = xrep_setup_rtbitmap(sc, rtb); + if (error) + return error; + } + + error = xchk_trans_alloc(sc, rtb->resblks); + if (error) + return error; + + error = xchk_install_live_inode(sc, rtg_bitmap(sc->sr.rtg)); + if (error) + return error; + + error = xchk_ino_dqattach(sc); + if (error) + return error; + + error = xchk_rtgroup_lock(sc, &sc->sr, XCHK_RTGLOCK_ALL); + if (error) + return error; + + /* + * Now that we've locked the rtbitmap, we can't race with growfsrt + * trying to expand the bitmap or change the size of the rt volume. + * Hence it is safe to compute and check the geometry values. + */ + if (mp->m_sb.sb_rblocks) { + rtb->rextents = xfs_blen_to_rtbxlen(mp, mp->m_sb.sb_rblocks); + rtb->rextslog = xfs_compute_rextslog(rtb->rextents); + rtb->rbmblocks = xfs_rtbitmap_blockcount(mp); + } + + return 0; +} + +/* Per-rtgroup bitmap contents. */ + +/* Cross-reference rtbitmap entries with other metadata. */ +STATIC void +xchk_rtbitmap_xref( + struct xchk_rtbitmap *rtb, + xfs_rtblock_t startblock, + xfs_rtblock_t blockcount) +{ + struct xfs_scrub *sc = rtb->sc; + xfs_rgblock_t rgbno = xfs_rtb_to_rgbno(sc->mp, startblock); + + if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT) + return; + if (!sc->sr.rmap_cur) + return; + + xchk_xref_has_no_rt_owner(sc, rgbno, blockcount); + xchk_xref_is_not_rt_shared(sc, rgbno, blockcount); + xchk_xref_is_not_rt_cow_staging(sc, rgbno, blockcount); + + if (rtb->next_free_rgbno < rgbno) + xchk_xref_has_rt_owner(sc, rtb->next_free_rgbno, + rgbno - rtb->next_free_rgbno); + rtb->next_free_rgbno = rgbno + blockcount; +} + +/* Scrub a free extent record from the realtime bitmap. */ +STATIC int +xchk_rtbitmap_rec( + struct xfs_rtgroup *rtg, + struct xfs_trans *tp, + const struct xfs_rtalloc_rec *rec, + void *priv) +{ + struct xchk_rtbitmap *rtb = priv; + struct xfs_scrub *sc = rtb->sc; + xfs_rtblock_t startblock; + xfs_filblks_t blockcount; + + startblock = xfs_rtx_to_rtb(rtg, rec->ar_startext); + blockcount = xfs_rtxlen_to_extlen(rtg_mount(rtg), rec->ar_extcount); + + if (!xfs_verify_rtbext(rtg_mount(rtg), startblock, blockcount)) + xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0); + + xchk_rtbitmap_xref(rtb, startblock, blockcount); + + if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT) + return -ECANCELED; + + return 0; +} + +/* Make sure the entire rtbitmap file is mapped with written extents. */ +STATIC int +xchk_rtbitmap_check_extents( + struct xfs_scrub *sc) +{ + struct xfs_bmbt_irec map; + struct xfs_iext_cursor icur; + struct xfs_mount *mp = sc->mp; + struct xfs_inode *ip = sc->ip; + xfs_fileoff_t off = 0; + xfs_fileoff_t endoff; + int error = 0; + + /* Mappings may not cross or lie beyond EOF. */ + endoff = XFS_B_TO_FSB(mp, ip->i_disk_size); + if (xfs_iext_lookup_extent(ip, &ip->i_df, endoff, &icur, &map)) { + xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, endoff); + return 0; + } + + while (off < endoff) { + int nmap = 1; + + if (xchk_should_terminate(sc, &error) || + (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)) + break; + + /* Make sure we have a written extent. */ + error = xfs_bmapi_read(ip, off, endoff - off, &map, &nmap, + XFS_DATA_FORK); + if (!xchk_fblock_process_error(sc, XFS_DATA_FORK, off, &error)) + break; + + if (nmap != 1 || !xfs_bmap_is_written_extent(&map)) { + xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, off); + break; + } + + off += map.br_blockcount; + } + + return error; +} + +/* Scrub this group's realtime bitmap. */ +int +xchk_rtbitmap( + struct xfs_scrub *sc) +{ + struct xfs_mount *mp = sc->mp; + struct xfs_rtgroup *rtg = sc->sr.rtg; + struct xfs_inode *rbmip = rtg_bitmap(rtg); + struct xchk_rtbitmap *rtb = sc->buf; + xfs_rgblock_t last_rgbno; + int error; + + /* Is sb_rextents correct? */ + if (mp->m_sb.sb_rextents != rtb->rextents) { + xchk_ip_set_corrupt(sc, rbmip); + return 0; + } + + /* Is sb_rextslog correct? */ + if (mp->m_sb.sb_rextslog != rtb->rextslog) { + xchk_ip_set_corrupt(sc, rbmip); + return 0; + } + + /* + * Is sb_rbmblocks large enough to handle the current rt volume? In no + * case can we exceed 4bn bitmap blocks since the super field is a u32. + */ + if (rtb->rbmblocks > U32_MAX) { + xchk_ip_set_corrupt(sc, rbmip); + return 0; + } + if (mp->m_sb.sb_rbmblocks != rtb->rbmblocks) { + xchk_ip_set_corrupt(sc, rbmip); + return 0; + } + + /* The bitmap file length must be aligned to an fsblock. */ + if (rbmip->i_disk_size & mp->m_blockmask) { + xchk_ip_set_corrupt(sc, rbmip); + return 0; + } + + /* + * Is the bitmap file itself large enough to handle the rt volume? + * growfsrt expands the bitmap file before updating sb_rextents, so the + * file can be larger than sb_rbmblocks. + */ + if (rbmip->i_disk_size < XFS_FSB_TO_B(mp, rtb->rbmblocks)) { + xchk_ip_set_corrupt(sc, rbmip); + return 0; + } + + /* Invoke the fork scrubber. */ + error = xchk_metadata_inode_forks(sc); + if (error || (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)) + return error; + + error = xchk_rtbitmap_check_extents(sc); + if (error || (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)) + return error; + + rtb->next_free_rgbno = 0; + error = xfs_rtalloc_query_all(rtg, sc->tp, xchk_rtbitmap_rec, rtb); + if (!xchk_fblock_process_error(sc, XFS_DATA_FORK, 0, &error)) + return error; + + /* + * Check that the are rmappings for all rt extents between the end of + * the last free extent we saw and the last possible extent in the rt + * group. + */ + last_rgbno = rtg->rtg_extents * mp->m_sb.sb_rextsize; + if (rtb->next_free_rgbno < last_rgbno) + xchk_xref_has_rt_owner(sc, rtb->next_free_rgbno, + last_rgbno - rtb->next_free_rgbno); + return 0; +} + +/* xref check that the extent is not free in the rtbitmap */ +void +xchk_xref_is_used_rt_space( + struct xfs_scrub *sc, + xfs_rtblock_t rtbno, + xfs_extlen_t len) +{ + struct xfs_rtgroup *rtg = sc->sr.rtg; + xfs_rtxnum_t startext; + xfs_rtxnum_t endext; + bool is_free; + int error; + + if (xchk_skip_xref(sc->sm)) + return; + + if (xfs_has_zoned(sc->mp)) { + if (!xfs_zone_rgbno_is_valid(rtg, + xfs_rtb_to_rgbno(sc->mp, rtbno) + len - 1)) + xchk_ip_xref_set_corrupt(sc, rtg_rmap(rtg)); + return; + } + + startext = xfs_rtb_to_rtx(sc->mp, rtbno); + endext = xfs_rtb_to_rtx(sc->mp, rtbno + len - 1); + error = xfs_rtalloc_extent_is_free(rtg, sc->tp, startext, + endext - startext + 1, &is_free); + if (!xchk_should_check_xref(sc, &error, NULL)) + return; + if (is_free) + xchk_ip_xref_set_corrupt(sc, rtg_bitmap(rtg)); +} -- cgit v1.3.1