x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

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) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 148 insertions, 0 deletions

diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
new file mode 100644
index 000000000..e104a651c
--- /dev/null
+++ b/drivers/md/dm-verity.h
@@ -0,0 +1,148 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ * Copyright (C) 2015 Google, Inc.
+ *
+ * Author: Mikulas Patocka <mpatocka@redhat.com>
+ *
+ * Based on Chromium dm-verity driver (C) 2011 The Chromium OS Authors
+ */
+
+#ifndef DM_VERITY_H
+#define DM_VERITY_H
+
+#include <linux/dm-io.h>
+#include <linux/dm-bufio.h>
+#include <linux/device-mapper.h>
+#include <linux/interrupt.h>
+#include <crypto/hash.h>
+#include <crypto/sha2.h>
+
+#define DM_VERITY_MAX_LEVELS		63
+
+enum verity_mode {
+	DM_VERITY_MODE_EIO,
+	DM_VERITY_MODE_LOGGING,
+	DM_VERITY_MODE_RESTART,
+	DM_VERITY_MODE_PANIC
+};
+
+enum verity_block_type {
+	DM_VERITY_BLOCK_TYPE_DATA,
+	DM_VERITY_BLOCK_TYPE_METADATA
+};
+
+struct dm_verity_fec;
+
+struct dm_verity {
+	struct dm_dev *data_dev;
+	struct dm_dev *hash_dev;
+	struct dm_target *ti;
+	struct dm_bufio_client *bufio;
+	char *alg_name;
+	struct crypto_shash *shash_tfm;
+	u8 *root_digest;	/* digest of the root block */
+	u8 *salt;		/* salt: its size is salt_size */
+	union {
+		struct sha256_ctx *sha256;	/* for use_sha256_lib=1 */
+		u8 *shash;			/* for use_sha256_lib=0 */
+	} initial_hashstate; /* salted initial state, if version >= 1 */
+	u8 *zero_digest;	/* digest for a zero block */
+#ifdef CONFIG_SECURITY
+	u8 *root_digest_sig;	/* signature of the root digest */
+	unsigned int sig_size;	/* root digest signature size */
+#endif /* CONFIG_SECURITY */
+	unsigned int salt_size;
+	sector_t hash_start;	/* index of first hash block on hash_dev */
+	sector_t hash_end;	/* 1 + index of last hash block on hash dev */
+	sector_t data_blocks;	/* the number of data blocks */
+	unsigned char data_dev_block_bits;	/* log2(data blocksize) */
+	unsigned char hash_dev_block_bits;	/* log2(hash blocksize) */
+	unsigned char hash_per_block_bits;	/* log2(hashes in hash block) */
+	unsigned char levels;	/* the number of tree levels */
+	unsigned char version;
+	bool hash_failed:1;	/* set if hash of any block failed */
+	bool use_bh_wq:1;	/* try to verify in BH wq before normal work-queue */
+	bool use_sha256_lib:1;	/* use SHA-256 library instead of generic crypto API */
+	bool use_sha256_finup_2x:1; /* use interleaved hashing optimization */
+	unsigned int digest_size;	/* digest size for the current hash algorithm */
+	enum verity_mode mode;	/* mode for handling verification errors */
+	enum verity_mode error_mode;/* mode for handling I/O errors */
+	atomic_t corrupted_errs;/* Number of errors for corrupted blocks */
+
+	struct workqueue_struct *verify_wq;
+
+	/* starting blocks for each tree level. 0 is the lowest level. */
+	sector_t hash_level_block[DM_VERITY_MAX_LEVELS];
+
+	struct dm_verity_fec *fec;	/* forward error correction */
+	unsigned long *validated_blocks; /* bitset blocks validated */
+
+	char *signature_key_desc; /* signature keyring reference */
+
+	struct dm_io_client *io;
+	mempool_t recheck_pool;
+};
+
+struct pending_block {
+	void *data;
+	sector_t blkno;
+	u8 want_digest[HASH_MAX_DIGESTSIZE];
+	u8 real_digest[HASH_MAX_DIGESTSIZE];
+};
+
+struct dm_verity_io {
+	struct dm_verity *v;
+
+	/* original value of bio->bi_end_io */
+	bio_end_io_t *orig_bi_end_io;
+
+	struct bvec_iter iter;
+
+	sector_t block;
+	unsigned int n_blocks;
+	bool in_bh;
+	bool had_mismatch;
+
+#ifdef CONFIG_DM_VERITY_FEC
+	struct dm_verity_fec_io *fec_io;
+#endif
+
+	struct work_struct work;
+
+	u8 tmp_digest[HASH_MAX_DIGESTSIZE];
+
+	/*
+	 * This is the queue of data blocks that are pending verification.  When
+	 * the crypto layer supports interleaved hashing, we allow multiple
+	 * blocks to be queued up in order to utilize it.  This can improve
+	 * performance significantly vs. sequential hashing of each block.
+	 */
+	int num_pending;
+	struct pending_block pending_blocks[2];
+
+	/*
+	 * Temporary space for hashing.  Either sha256 or shash is used,
+	 * depending on the value of use_sha256_lib.  If shash is used,
+	 * then this field is variable-length, with total size
+	 * sizeof(struct shash_desc) + crypto_shash_descsize(shash_tfm).
+	 * For this reason, this field must be the end of the struct.
+	 */
+	union {
+		struct sha256_ctx sha256;
+		struct shash_desc shash;
+	} hash_ctx;
+};
+
+extern int verity_hash(struct dm_verity *v, struct dm_verity_io *io,
+		       const u8 *data, size_t len, u8 *digest);
+
+extern int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,
+				 sector_t block, u8 *digest, bool *is_zero);
+
+extern bool dm_is_verity_target(struct dm_target *ti);
+extern int dm_verity_get_mode(struct dm_target *ti);
+extern int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest,
+				     unsigned int *digest_size);
+
+#endif /* DM_VERITY_H */