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/fuse/iomode.c | 275 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 275 insertions(+) create mode 100644 fs/fuse/iomode.c (limited to 'fs/fuse/iomode.c') diff --git a/fs/fuse/iomode.c b/fs/fuse/iomode.c new file mode 100644 index 000000000..372893318 --- /dev/null +++ b/fs/fuse/iomode.c @@ -0,0 +1,275 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * FUSE inode io modes. + * + * Copyright (c) 2024 CTERA Networks. + */ + +#include "fuse_i.h" + +#include +#include +#include +#include + +/* + * Return true if need to wait for new opens in caching mode. + */ +static inline bool fuse_is_io_cache_wait(struct fuse_inode *fi) +{ + return READ_ONCE(fi->iocachectr) < 0 && !fuse_inode_backing(fi); +} + +/* + * Called on cached file open() and on first mmap() of direct_io file. + * Takes cached_io inode mode reference to be dropped on file release. + * + * Blocks new parallel dio writes and waits for the in-progress parallel dio + * writes to complete. + */ +int fuse_file_cached_io_open(struct inode *inode, struct fuse_file *ff) +{ + struct fuse_inode *fi = get_fuse_inode(inode); + + /* There are no io modes if server does not implement open */ + if (!ff->args) + return 0; + + spin_lock(&fi->lock); + /* + * Setting the bit advises new direct-io writes to use an exclusive + * lock - without it the wait below might be forever. + */ + while (fuse_is_io_cache_wait(fi)) { + set_bit(FUSE_I_CACHE_IO_MODE, &fi->state); + spin_unlock(&fi->lock); + wait_event(fi->direct_io_waitq, !fuse_is_io_cache_wait(fi)); + spin_lock(&fi->lock); + } + + /* + * Check if inode entered passthrough io mode while waiting for parallel + * dio write completion. + */ + if (fuse_inode_backing(fi)) { + clear_bit(FUSE_I_CACHE_IO_MODE, &fi->state); + spin_unlock(&fi->lock); + return -ETXTBSY; + } + + WARN_ON(ff->iomode == IOM_UNCACHED); + if (ff->iomode == IOM_NONE) { + ff->iomode = IOM_CACHED; + if (fi->iocachectr == 0) + set_bit(FUSE_I_CACHE_IO_MODE, &fi->state); + fi->iocachectr++; + } + spin_unlock(&fi->lock); + return 0; +} + +static void fuse_file_cached_io_release(struct fuse_file *ff, + struct fuse_inode *fi) +{ + spin_lock(&fi->lock); + WARN_ON(fi->iocachectr <= 0); + WARN_ON(ff->iomode != IOM_CACHED); + ff->iomode = IOM_NONE; + fi->iocachectr--; + if (fi->iocachectr == 0) + clear_bit(FUSE_I_CACHE_IO_MODE, &fi->state); + spin_unlock(&fi->lock); +} + +/* Start strictly uncached io mode where cache access is not allowed */ +int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb) +{ + struct fuse_backing *oldfb; + int err = 0; + + spin_lock(&fi->lock); + /* deny conflicting backing files on same fuse inode */ + oldfb = fuse_inode_backing(fi); + if (fb && oldfb && oldfb != fb) { + err = -EBUSY; + goto unlock; + } + if (fi->iocachectr > 0) { + err = -ETXTBSY; + goto unlock; + } + fi->iocachectr--; + + /* fuse inode holds a single refcount of backing file */ + if (fb && !oldfb) { + oldfb = fuse_inode_backing_set(fi, fb); + WARN_ON_ONCE(oldfb != NULL); + } else { + fuse_backing_put(fb); + } +unlock: + spin_unlock(&fi->lock); + return err; +} + +/* Takes uncached_io inode mode reference to be dropped on file release */ +static int fuse_file_uncached_io_open(struct inode *inode, + struct fuse_file *ff, + struct fuse_backing *fb) +{ + struct fuse_inode *fi = get_fuse_inode(inode); + int err; + + err = fuse_inode_uncached_io_start(fi, fb); + if (err) + return err; + + WARN_ON(ff->iomode != IOM_NONE); + ff->iomode = IOM_UNCACHED; + return 0; +} + +void fuse_inode_uncached_io_end(struct fuse_inode *fi) +{ + struct fuse_backing *oldfb = NULL; + + spin_lock(&fi->lock); + WARN_ON(fi->iocachectr >= 0); + fi->iocachectr++; + if (!fi->iocachectr) { + wake_up(&fi->direct_io_waitq); + oldfb = fuse_inode_backing_set(fi, NULL); + } + spin_unlock(&fi->lock); + if (oldfb) + fuse_backing_put(oldfb); +} + +/* Drop uncached_io reference from passthrough open */ +static void fuse_file_uncached_io_release(struct fuse_file *ff, + struct fuse_inode *fi) +{ + WARN_ON(ff->iomode != IOM_UNCACHED); + ff->iomode = IOM_NONE; + fuse_inode_uncached_io_end(fi); +} + +/* + * Open flags that are allowed in combination with FOPEN_PASSTHROUGH. + * A combination of FOPEN_PASSTHROUGH and FOPEN_DIRECT_IO means that read/write + * operations go directly to the server, but mmap is done on the backing file. + * FOPEN_PASSTHROUGH mode should not co-exist with any users of the fuse inode + * page cache, so FOPEN_KEEP_CACHE is a strange and undesired combination. + */ +#define FOPEN_PASSTHROUGH_MASK \ + (FOPEN_PASSTHROUGH | FOPEN_DIRECT_IO | FOPEN_PARALLEL_DIRECT_WRITES | \ + FOPEN_NOFLUSH) + +static int fuse_file_passthrough_open(struct inode *inode, struct file *file) +{ + struct fuse_file *ff = file->private_data; + struct fuse_conn *fc = get_fuse_conn(inode); + struct fuse_backing *fb; + int err; + + /* Check allowed conditions for file open in passthrough mode */ + if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH) || !fc->passthrough || + (ff->open_flags & ~FOPEN_PASSTHROUGH_MASK)) + return -EINVAL; + + fb = fuse_passthrough_open(file, ff->args->open_outarg.backing_id); + if (IS_ERR(fb)) + return PTR_ERR(fb); + + /* First passthrough file open denies caching inode io mode */ + err = fuse_file_uncached_io_open(inode, ff, fb); + if (!err) + return 0; + + fuse_passthrough_release(ff, fb); + fuse_backing_put(fb); + + return err; +} + +/* Request access to submit new io to inode via open file */ +int fuse_file_io_open(struct file *file, struct inode *inode) +{ + struct fuse_file *ff = file->private_data; + struct fuse_inode *fi = get_fuse_inode(inode); + int err; + + /* + * io modes are not relevant with DAX and with server that does not + * implement open. + */ + if (FUSE_IS_DAX(inode) || !ff->args) + return 0; + + /* + * Server is expected to use FOPEN_PASSTHROUGH for all opens of an inode + * which is already open for passthrough. + */ + err = -EINVAL; + if (fuse_inode_backing(fi) && !(ff->open_flags & FOPEN_PASSTHROUGH)) + goto fail; + + /* + * FOPEN_PARALLEL_DIRECT_WRITES requires FOPEN_DIRECT_IO. + */ + if (!(ff->open_flags & FOPEN_DIRECT_IO)) + ff->open_flags &= ~FOPEN_PARALLEL_DIRECT_WRITES; + + /* + * First passthrough file open denies caching inode io mode. + * First caching file open enters caching inode io mode. + * + * Note that if user opens a file open with O_DIRECT, but server did + * not specify FOPEN_DIRECT_IO, a later fcntl() could remove O_DIRECT, + * so we put the inode in caching mode to prevent parallel dio. + */ + if ((ff->open_flags & FOPEN_DIRECT_IO) && + !(ff->open_flags & FOPEN_PASSTHROUGH)) + return 0; + + if (ff->open_flags & FOPEN_PASSTHROUGH) + err = fuse_file_passthrough_open(inode, file); + else + err = fuse_file_cached_io_open(inode, ff); + if (err) + goto fail; + + return 0; + +fail: + pr_debug("failed to open file in requested io mode (open_flags=0x%x, err=%i).\n", + ff->open_flags, err); + /* + * The file open mode determines the inode io mode. + * Using incorrect open mode is a server mistake, which results in + * user visible failure of open() with EIO error. + */ + return -EIO; +} + +/* No more pending io and no new io possible to inode via open/mmapped file */ +void fuse_file_io_release(struct fuse_file *ff, struct inode *inode) +{ + struct fuse_inode *fi = get_fuse_inode(inode); + + /* + * Last passthrough file close allows caching inode io mode. + * Last caching file close exits caching inode io mode. + */ + switch (ff->iomode) { + case IOM_NONE: + /* Nothing to do */ + break; + case IOM_UNCACHED: + fuse_file_uncached_io_release(ff, fi); + break; + case IOM_CACHED: + fuse_file_cached_io_release(ff, fi); + break; + } +} -- cgit v1.3.1