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/minix/itree_common.c | 374 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 374 insertions(+) create mode 100644 fs/minix/itree_common.c (limited to 'fs/minix/itree_common.c') diff --git a/fs/minix/itree_common.c b/fs/minix/itree_common.c new file mode 100644 index 000000000..c3cd2c75a --- /dev/null +++ b/fs/minix/itree_common.c @@ -0,0 +1,374 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Generic part */ + +typedef struct { + block_t *p; + block_t key; + struct buffer_head *bh; +} Indirect; + +static DEFINE_RWLOCK(pointers_lock); + +static inline void add_chain(Indirect *p, struct buffer_head *bh, block_t *v) +{ + p->key = *(p->p = v); + p->bh = bh; +} + +static inline int verify_chain(Indirect *from, Indirect *to) +{ + while (from <= to && from->key == *from->p) + from++; + return (from > to); +} + +static inline block_t *block_end(struct buffer_head *bh) +{ + return (block_t *)((char*)bh->b_data + bh->b_size); +} + +static inline Indirect *get_branch(struct inode *inode, + int depth, + int *offsets, + Indirect chain[DEPTH], + int *err) +{ + struct super_block *sb = inode->i_sb; + Indirect *p = chain; + struct buffer_head *bh; + + *err = 0; + /* i_data is not going away, no lock needed */ + add_chain (chain, NULL, i_data(inode) + *offsets); + if (!p->key) + goto no_block; + while (--depth) { + bh = sb_bread(sb, block_to_cpu(p->key)); + if (!bh) + goto failure; + read_lock(&pointers_lock); + if (!verify_chain(chain, p)) + goto changed; + add_chain(++p, bh, (block_t *)bh->b_data + *++offsets); + read_unlock(&pointers_lock); + if (!p->key) + goto no_block; + } + return NULL; + +changed: + read_unlock(&pointers_lock); + brelse(bh); + *err = -EAGAIN; + goto no_block; +failure: + *err = -EIO; +no_block: + return p; +} + +static int alloc_branch(struct inode *inode, + int num, + int *offsets, + Indirect *branch) +{ + int n = 0; + int i; + int parent = minix_new_block(inode); + int err = -ENOSPC; + + branch[0].key = cpu_to_block(parent); + if (parent) for (n = 1; n < num; n++) { + struct buffer_head *bh; + /* Allocate the next block */ + int nr = minix_new_block(inode); + if (!nr) + break; + branch[n].key = cpu_to_block(nr); + bh = sb_getblk(inode->i_sb, parent); + if (!bh) { + minix_free_block(inode, nr); + err = -ENOMEM; + break; + } + lock_buffer(bh); + memset(bh->b_data, 0, bh->b_size); + branch[n].bh = bh; + branch[n].p = (block_t*) bh->b_data + offsets[n]; + *branch[n].p = branch[n].key; + set_buffer_uptodate(bh); + unlock_buffer(bh); + mmb_mark_buffer_dirty(bh, &minix_i(inode)->i_metadata_bhs); + parent = nr; + } + if (n == num) + return 0; + + /* Allocation failed, free what we already allocated */ + for (i = 1; i < n; i++) + bforget(branch[i].bh); + for (i = 0; i < n; i++) + minix_free_block(inode, block_to_cpu(branch[i].key)); + return err; +} + +static inline int splice_branch(struct inode *inode, + Indirect chain[DEPTH], + Indirect *where, + int num) +{ + int i; + + write_lock(&pointers_lock); + + /* Verify that place we are splicing to is still there and vacant */ + if (!verify_chain(chain, where-1) || *where->p) + goto changed; + + *where->p = where->key; + + write_unlock(&pointers_lock); + + /* We are done with atomic stuff, now do the rest of housekeeping */ + + inode_set_ctime_current(inode); + + /* had we spliced it onto indirect block? */ + if (where->bh) + mmb_mark_buffer_dirty(where->bh, + &minix_i(inode)->i_metadata_bhs); + + mark_inode_dirty(inode); + return 0; + +changed: + write_unlock(&pointers_lock); + for (i = 1; i < num; i++) + bforget(where[i].bh); + for (i = 0; i < num; i++) + minix_free_block(inode, block_to_cpu(where[i].key)); + return -EAGAIN; +} + +static int get_block(struct inode * inode, sector_t block, + struct buffer_head *bh, int create) +{ + int err = -EIO; + int offsets[DEPTH]; + Indirect chain[DEPTH]; + Indirect *partial; + int left; + int depth = block_to_path(inode, block, offsets); + + if (depth == 0) + goto out; + +reread: + partial = get_branch(inode, depth, offsets, chain, &err); + + /* Simplest case - block found, no allocation needed */ + if (!partial) { +got_it: + map_bh(bh, inode->i_sb, block_to_cpu(chain[depth-1].key)); + /* Clean up and exit */ + partial = chain+depth-1; /* the whole chain */ + goto cleanup; + } + + /* Next simple case - plain lookup or failed read of indirect block */ + if (!create || err == -EIO) { +cleanup: + while (partial > chain) { + brelse(partial->bh); + partial--; + } +out: + return err; + } + + /* + * Indirect block might be removed by truncate while we were + * reading it. Handling of that case (forget what we've got and + * reread) is taken out of the main path. + */ + if (err == -EAGAIN) + goto changed; + + left = (chain + depth) - partial; + err = alloc_branch(inode, left, offsets+(partial-chain), partial); + if (err) + goto cleanup; + + if (splice_branch(inode, chain, partial, left) < 0) + goto changed; + + set_buffer_new(bh); + goto got_it; + +changed: + while (partial > chain) { + brelse(partial->bh); + partial--; + } + goto reread; +} + +static inline int all_zeroes(block_t *p, block_t *q) +{ + while (p < q) + if (*p++) + return 0; + return 1; +} + +static Indirect *find_shared(struct inode *inode, + int depth, + int offsets[DEPTH], + Indirect chain[DEPTH], + block_t *top) +{ + Indirect *partial, *p; + int k, err; + + *top = 0; + for (k = depth; k > 1 && !offsets[k-1]; k--) + ; + partial = get_branch(inode, k, offsets, chain, &err); + + write_lock(&pointers_lock); + if (!partial) + partial = chain + k-1; + if (!partial->key && *partial->p) { + write_unlock(&pointers_lock); + goto no_top; + } + for (p=partial;p>chain && all_zeroes((block_t*)p->bh->b_data,p->p);p--) + ; + if (p == chain + k - 1 && p > chain) { + p->p--; + } else { + *top = *p->p; + *p->p = 0; + } + write_unlock(&pointers_lock); + + while(partial > p) + { + brelse(partial->bh); + partial--; + } +no_top: + return partial; +} + +static inline void free_data(struct inode *inode, block_t *p, block_t *q) +{ + unsigned long nr; + + for ( ; p < q ; p++) { + nr = block_to_cpu(*p); + if (nr) { + *p = 0; + minix_free_block(inode, nr); + } + } +} + +static void free_branches(struct inode *inode, block_t *p, block_t *q, int depth) +{ + struct buffer_head * bh; + unsigned long nr; + + if (depth--) { + for ( ; p < q ; p++) { + nr = block_to_cpu(*p); + if (!nr) + continue; + *p = 0; + bh = sb_bread(inode->i_sb, nr); + if (!bh) + continue; + free_branches(inode, (block_t*)bh->b_data, + block_end(bh), depth); + bforget(bh); + minix_free_block(inode, nr); + mark_inode_dirty(inode); + } + } else + free_data(inode, p, q); +} + +static inline void truncate (struct inode * inode) +{ + struct super_block *sb = inode->i_sb; + block_t *idata = i_data(inode); + int offsets[DEPTH]; + Indirect chain[DEPTH]; + Indirect *partial; + block_t nr = 0; + int n; + int first_whole; + long iblock; + + iblock = (inode->i_size + sb->s_blocksize -1) >> sb->s_blocksize_bits; + block_truncate_page(inode->i_mapping, inode->i_size, get_block); + + n = block_to_path(inode, iblock, offsets); + if (!n) + return; + + if (n == 1) { + free_data(inode, idata+offsets[0], idata + DIRECT); + first_whole = 0; + goto do_indirects; + } + + first_whole = offsets[0] + 1 - DIRECT; + partial = find_shared(inode, n, offsets, chain, &nr); + if (nr) { + if (partial == chain) + mark_inode_dirty(inode); + else + mmb_mark_buffer_dirty(partial->bh, + &minix_i(inode)->i_metadata_bhs); + free_branches(inode, &nr, &nr+1, (chain+n-1) - partial); + } + /* Clear the ends of indirect blocks on the shared branch */ + while (partial > chain) { + free_branches(inode, partial->p + 1, block_end(partial->bh), + (chain+n-1) - partial); + mmb_mark_buffer_dirty(partial->bh, + &minix_i(inode)->i_metadata_bhs); + brelse (partial->bh); + partial--; + } +do_indirects: + /* Kill the remaining (whole) subtrees */ + while (first_whole < DEPTH-1) { + nr = idata[DIRECT+first_whole]; + if (nr) { + idata[DIRECT+first_whole] = 0; + mark_inode_dirty(inode); + free_branches(inode, &nr, &nr+1, first_whole+1); + } + first_whole++; + } + inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode)); + mark_inode_dirty(inode); +} + +static inline unsigned nblocks(loff_t size, struct super_block *sb) +{ + int k = sb->s_blocksize_bits - 10; + unsigned blocks, res, direct = DIRECT, i = DEPTH; + blocks = (size + sb->s_blocksize - 1) >> (BLOCK_SIZE_BITS + k); + res = blocks; + while (--i && blocks > direct) { + blocks -= direct; + blocks += sb->s_blocksize/sizeof(block_t) - 1; + blocks /= sb->s_blocksize/sizeof(block_t); + res += blocks; + direct = 1; + } + return res; +} -- cgit v1.3.1