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 --- drivers/md/bcache/debug.c | 262 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 262 insertions(+) create mode 100644 drivers/md/bcache/debug.c (limited to 'drivers/md/bcache/debug.c') diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c new file mode 100644 index 000000000..2691a5da3 --- /dev/null +++ b/drivers/md/bcache/debug.c @@ -0,0 +1,262 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Assorted bcache debug code + * + * Copyright 2010, 2011 Kent Overstreet + * Copyright 2012 Google, Inc. + */ + +#include "bcache.h" +#include "btree.h" +#include "debug.h" +#include "extents.h" + +#include +#include +#include +#include +#include + +struct dentry *bcache_debug; + +#ifdef CONFIG_BCACHE_DEBUG + +#define for_each_written_bset(b, start, i) \ + for (i = (start); \ + (void *) i < (void *) (start) + (KEY_SIZE(&b->key) << 9) &&\ + i->seq == (start)->seq; \ + i = (void *) i + set_blocks(i, block_bytes(b->c->cache)) * \ + block_bytes(b->c->cache)) + +void bch_btree_verify(struct btree *b) +{ + struct btree *v = b->c->verify_data; + struct bset *ondisk, *sorted, *inmemory; + struct bio *bio; + + if (!b->c->verify || !b->c->verify_ondisk) + return; + + down(&b->io_mutex); + mutex_lock(&b->c->verify_lock); + + ondisk = b->c->verify_ondisk; + sorted = b->c->verify_data->keys.set->data; + inmemory = b->keys.set->data; + + bkey_copy(&v->key, &b->key); + v->written = 0; + v->level = b->level; + v->keys.ops = b->keys.ops; + + bio = bch_bbio_alloc(b->c); + bio_set_dev(bio, b->c->cache->bdev); + bio->bi_iter.bi_sector = PTR_OFFSET(&b->key, 0); + bio->bi_iter.bi_size = KEY_SIZE(&v->key) << 9; + bio->bi_opf = REQ_OP_READ | REQ_META; + bch_bio_map(bio, sorted); + + submit_bio_wait(bio); + bch_bbio_free(bio, b->c); + + memcpy(ondisk, sorted, KEY_SIZE(&v->key) << 9); + + bch_btree_node_read_done(v); + sorted = v->keys.set->data; + + if (inmemory->keys != sorted->keys || + memcmp(inmemory->start, + sorted->start, + (void *) bset_bkey_last(inmemory) - + (void *) inmemory->start)) { + struct bset *i; + unsigned int j; + + console_lock(); + + pr_err("*** in memory:\n"); + bch_dump_bset(&b->keys, inmemory, 0); + + pr_err("*** read back in:\n"); + bch_dump_bset(&v->keys, sorted, 0); + + for_each_written_bset(b, ondisk, i) { + unsigned int block = ((void *) i - (void *) ondisk) / + block_bytes(b->c->cache); + + pr_err("*** on disk block %u:\n", block); + bch_dump_bset(&b->keys, i, block); + } + + pr_err("*** block %zu not written\n", + ((void *) i - (void *) ondisk) / block_bytes(b->c->cache)); + + for (j = 0; j < inmemory->keys; j++) + if (inmemory->d[j] != sorted->d[j]) + break; + + pr_err("b->written %u\n", b->written); + + console_unlock(); + panic("verify failed at %u\n", j); + } + + mutex_unlock(&b->c->verify_lock); + up(&b->io_mutex); +} + +void bch_data_verify(struct cached_dev *dc, struct bio *bio) +{ + unsigned int nr_segs = bio_segments(bio); + struct bio *check; + struct bio_vec bv, cbv; + struct bvec_iter iter, citer = { 0 }; + + check = bio_kmalloc(nr_segs, GFP_NOIO); + if (!check) + return; + bio_init_inline(check, bio->bi_bdev, nr_segs, REQ_OP_READ); + check->bi_iter.bi_sector = bio->bi_iter.bi_sector; + check->bi_iter.bi_size = bio->bi_iter.bi_size; + + bch_bio_map(check, NULL); + if (bch_bio_alloc_pages(check, GFP_NOIO)) + goto out_put; + + submit_bio_wait(check); + + citer.bi_size = UINT_MAX; + bio_for_each_segment(bv, bio, iter) { + void *p1 = bvec_kmap_local(&bv); + void *p2; + + cbv = bio_iter_iovec(check, citer); + p2 = bvec_kmap_local(&cbv); + + cache_set_err_on(memcmp(p1, p2, bv.bv_len), + dc->disk.c, + "verify failed at dev %pg sector %llu", + dc->bdev, + (uint64_t) bio->bi_iter.bi_sector); + + kunmap_local(p2); + kunmap_local(p1); + bio_advance_iter(check, &citer, bv.bv_len); + } + + bio_free_pages(check); +out_put: + bio_uninit(check); + kfree(check); +} + +#endif + +#ifdef CONFIG_DEBUG_FS + +/* XXX: cache set refcounting */ + +struct dump_iterator { + char buf[PAGE_SIZE]; + size_t bytes; + struct cache_set *c; + struct keybuf keys; +}; + +static bool dump_pred(struct keybuf *buf, struct bkey *k) +{ + return true; +} + +static ssize_t bch_dump_read(struct file *file, char __user *buf, + size_t size, loff_t *ppos) +{ + struct dump_iterator *i = file->private_data; + ssize_t ret = 0; + char kbuf[80]; + + while (size) { + struct keybuf_key *w; + unsigned int bytes = min(i->bytes, size); + + if (copy_to_user(buf, i->buf, bytes)) + return -EFAULT; + + ret += bytes; + buf += bytes; + size -= bytes; + i->bytes -= bytes; + memmove(i->buf, i->buf + bytes, i->bytes); + + if (i->bytes) + break; + + w = bch_keybuf_next_rescan(i->c, &i->keys, &MAX_KEY, dump_pred); + if (!w) + break; + + bch_extent_to_text(kbuf, sizeof(kbuf), &w->key); + i->bytes = snprintf(i->buf, PAGE_SIZE, "%s\n", kbuf); + bch_keybuf_del(&i->keys, w); + } + + return ret; +} + +static int bch_dump_open(struct inode *inode, struct file *file) +{ + struct cache_set *c = inode->i_private; + struct dump_iterator *i; + + i = kzalloc_obj(struct dump_iterator); + if (!i) + return -ENOMEM; + + file->private_data = i; + i->c = c; + bch_keybuf_init(&i->keys); + i->keys.last_scanned = KEY(0, 0, 0); + + return 0; +} + +static int bch_dump_release(struct inode *inode, struct file *file) +{ + kfree(file->private_data); + return 0; +} + +static const struct file_operations cache_set_debug_ops = { + .owner = THIS_MODULE, + .open = bch_dump_open, + .read = bch_dump_read, + .release = bch_dump_release +}; + +void bch_debug_init_cache_set(struct cache_set *c) +{ + if (!IS_ERR_OR_NULL(bcache_debug)) { + char name[50]; + + snprintf(name, 50, "bcache-%pU", c->set_uuid); + c->debug = debugfs_create_file(name, 0400, bcache_debug, c, + &cache_set_debug_ops); + } +} + +#endif + +void bch_debug_exit(void) +{ + debugfs_remove_recursive(bcache_debug); +} + +void __init bch_debug_init(void) +{ + /* + * it is unnecessary to check return value of + * debugfs_create_file(), we should not care + * about this. + */ + bcache_debug = debugfs_create_dir("bcache", NULL); +} -- cgit v1.3.1