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, 302 insertions, 0 deletions

diff --git a/lib/crypto/md5.c b/lib/crypto/md5.c
new file mode 100644
index 000000000..3d2b017a0
--- /dev/null
+++ b/lib/crypto/md5.c
@@ -0,0 +1,302 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * MD5 and HMAC-MD5 library functions
+ *
+ * md5_block() is derived from cryptoapi implementation, originally based on the
+ * public domain implementation written by Colin Plumb in 1993.
+ *
+ * Copyright (c) Cryptoapi developers.
+ * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
+ * Copyright 2025 Google LLC
+ */
+
+#include <crypto/hmac.h>
+#include <crypto/md5.h>
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/unaligned.h>
+#include <linux/wordpart.h>
+
+static const struct md5_block_state md5_iv = {
+	.h = { MD5_H0, MD5_H1, MD5_H2, MD5_H3 },
+};
+
+#define F1(x, y, z) (z ^ (x & (y ^ z)))
+#define F2(x, y, z) F1(z, x, y)
+#define F3(x, y, z) (x ^ y ^ z)
+#define F4(x, y, z) (y ^ (x | ~z))
+
+#define MD5STEP(f, w, x, y, z, in, s) \
+	(w += f(x, y, z) + in, w = rol32(w, s) + x)
+
+static void md5_block(struct md5_block_state *state,
+		      const u8 data[MD5_BLOCK_SIZE])
+{
+	u32 in[MD5_BLOCK_WORDS];
+	u32 a, b, c, d;
+
+	memcpy(in, data, MD5_BLOCK_SIZE);
+	le32_to_cpu_array(in, ARRAY_SIZE(in));
+
+	a = state->h[0];
+	b = state->h[1];
+	c = state->h[2];
+	d = state->h[3];
+
+	MD5STEP(F1, a, b, c, d, in[0] + 0xd76aa478, 7);
+	MD5STEP(F1, d, a, b, c, in[1] + 0xe8c7b756, 12);
+	MD5STEP(F1, c, d, a, b, in[2] + 0x242070db, 17);
+	MD5STEP(F1, b, c, d, a, in[3] + 0xc1bdceee, 22);
+	MD5STEP(F1, a, b, c, d, in[4] + 0xf57c0faf, 7);
+	MD5STEP(F1, d, a, b, c, in[5] + 0x4787c62a, 12);
+	MD5STEP(F1, c, d, a, b, in[6] + 0xa8304613, 17);
+	MD5STEP(F1, b, c, d, a, in[7] + 0xfd469501, 22);
+	MD5STEP(F1, a, b, c, d, in[8] + 0x698098d8, 7);
+	MD5STEP(F1, d, a, b, c, in[9] + 0x8b44f7af, 12);
+	MD5STEP(F1, c, d, a, b, in[10] + 0xffff5bb1, 17);
+	MD5STEP(F1, b, c, d, a, in[11] + 0x895cd7be, 22);
+	MD5STEP(F1, a, b, c, d, in[12] + 0x6b901122, 7);
+	MD5STEP(F1, d, a, b, c, in[13] + 0xfd987193, 12);
+	MD5STEP(F1, c, d, a, b, in[14] + 0xa679438e, 17);
+	MD5STEP(F1, b, c, d, a, in[15] + 0x49b40821, 22);
+
+	MD5STEP(F2, a, b, c, d, in[1] + 0xf61e2562, 5);
+	MD5STEP(F2, d, a, b, c, in[6] + 0xc040b340, 9);
+	MD5STEP(F2, c, d, a, b, in[11] + 0x265e5a51, 14);
+	MD5STEP(F2, b, c, d, a, in[0] + 0xe9b6c7aa, 20);
+	MD5STEP(F2, a, b, c, d, in[5] + 0xd62f105d, 5);
+	MD5STEP(F2, d, a, b, c, in[10] + 0x02441453, 9);
+	MD5STEP(F2, c, d, a, b, in[15] + 0xd8a1e681, 14);
+	MD5STEP(F2, b, c, d, a, in[4] + 0xe7d3fbc8, 20);
+	MD5STEP(F2, a, b, c, d, in[9] + 0x21e1cde6, 5);
+	MD5STEP(F2, d, a, b, c, in[14] + 0xc33707d6, 9);
+	MD5STEP(F2, c, d, a, b, in[3] + 0xf4d50d87, 14);
+	MD5STEP(F2, b, c, d, a, in[8] + 0x455a14ed, 20);
+	MD5STEP(F2, a, b, c, d, in[13] + 0xa9e3e905, 5);
+	MD5STEP(F2, d, a, b, c, in[2] + 0xfcefa3f8, 9);
+	MD5STEP(F2, c, d, a, b, in[7] + 0x676f02d9, 14);
+	MD5STEP(F2, b, c, d, a, in[12] + 0x8d2a4c8a, 20);
+
+	MD5STEP(F3, a, b, c, d, in[5] + 0xfffa3942, 4);
+	MD5STEP(F3, d, a, b, c, in[8] + 0x8771f681, 11);
+	MD5STEP(F3, c, d, a, b, in[11] + 0x6d9d6122, 16);
+	MD5STEP(F3, b, c, d, a, in[14] + 0xfde5380c, 23);
+	MD5STEP(F3, a, b, c, d, in[1] + 0xa4beea44, 4);
+	MD5STEP(F3, d, a, b, c, in[4] + 0x4bdecfa9, 11);
+	MD5STEP(F3, c, d, a, b, in[7] + 0xf6bb4b60, 16);
+	MD5STEP(F3, b, c, d, a, in[10] + 0xbebfbc70, 23);
+	MD5STEP(F3, a, b, c, d, in[13] + 0x289b7ec6, 4);
+	MD5STEP(F3, d, a, b, c, in[0] + 0xeaa127fa, 11);
+	MD5STEP(F3, c, d, a, b, in[3] + 0xd4ef3085, 16);
+	MD5STEP(F3, b, c, d, a, in[6] + 0x04881d05, 23);
+	MD5STEP(F3, a, b, c, d, in[9] + 0xd9d4d039, 4);
+	MD5STEP(F3, d, a, b, c, in[12] + 0xe6db99e5, 11);
+	MD5STEP(F3, c, d, a, b, in[15] + 0x1fa27cf8, 16);
+	MD5STEP(F3, b, c, d, a, in[2] + 0xc4ac5665, 23);
+
+	MD5STEP(F4, a, b, c, d, in[0] + 0xf4292244, 6);
+	MD5STEP(F4, d, a, b, c, in[7] + 0x432aff97, 10);
+	MD5STEP(F4, c, d, a, b, in[14] + 0xab9423a7, 15);
+	MD5STEP(F4, b, c, d, a, in[5] + 0xfc93a039, 21);
+	MD5STEP(F4, a, b, c, d, in[12] + 0x655b59c3, 6);
+	MD5STEP(F4, d, a, b, c, in[3] + 0x8f0ccc92, 10);
+	MD5STEP(F4, c, d, a, b, in[10] + 0xffeff47d, 15);
+	MD5STEP(F4, b, c, d, a, in[1] + 0x85845dd1, 21);
+	MD5STEP(F4, a, b, c, d, in[8] + 0x6fa87e4f, 6);
+	MD5STEP(F4, d, a, b, c, in[15] + 0xfe2ce6e0, 10);
+	MD5STEP(F4, c, d, a, b, in[6] + 0xa3014314, 15);
+	MD5STEP(F4, b, c, d, a, in[13] + 0x4e0811a1, 21);
+	MD5STEP(F4, a, b, c, d, in[4] + 0xf7537e82, 6);
+	MD5STEP(F4, d, a, b, c, in[11] + 0xbd3af235, 10);
+	MD5STEP(F4, c, d, a, b, in[2] + 0x2ad7d2bb, 15);
+	MD5STEP(F4, b, c, d, a, in[9] + 0xeb86d391, 21);
+
+	state->h[0] += a;
+	state->h[1] += b;
+	state->h[2] += c;
+	state->h[3] += d;
+}
+
+static void md5_blocks(struct md5_block_state *state,
+		       const u8 *data, size_t nblocks)
+{
+	do {
+		md5_block(state, data);
+		data += MD5_BLOCK_SIZE;
+	} while (--nblocks);
+}
+
+void md5_init(struct md5_ctx *ctx)
+{
+	ctx->state = md5_iv;
+	ctx->bytecount = 0;
+}
+EXPORT_SYMBOL_GPL(md5_init);
+
+void md5_update(struct md5_ctx *ctx, const u8 *data, size_t len)
+{
+	size_t partial = ctx->bytecount % MD5_BLOCK_SIZE;
+
+	ctx->bytecount += len;
+
+	if (partial + len >= MD5_BLOCK_SIZE) {
+		size_t nblocks;
+
+		if (partial) {
+			size_t l = MD5_BLOCK_SIZE - partial;
+
+			memcpy(&ctx->buf[partial], data, l);
+			data += l;
+			len -= l;
+
+			md5_blocks(&ctx->state, ctx->buf, 1);
+		}
+
+		nblocks = len / MD5_BLOCK_SIZE;
+		len %= MD5_BLOCK_SIZE;
+
+		if (nblocks) {
+			md5_blocks(&ctx->state, data, nblocks);
+			data += nblocks * MD5_BLOCK_SIZE;
+		}
+		partial = 0;
+	}
+	if (len)
+		memcpy(&ctx->buf[partial], data, len);
+}
+EXPORT_SYMBOL_GPL(md5_update);
+
+static void __md5_final(struct md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE])
+{
+	u64 bitcount = ctx->bytecount << 3;
+	size_t partial = ctx->bytecount % MD5_BLOCK_SIZE;
+
+	ctx->buf[partial++] = 0x80;
+	if (partial > MD5_BLOCK_SIZE - 8) {
+		memset(&ctx->buf[partial], 0, MD5_BLOCK_SIZE - partial);
+		md5_blocks(&ctx->state, ctx->buf, 1);
+		partial = 0;
+	}
+	memset(&ctx->buf[partial], 0, MD5_BLOCK_SIZE - 8 - partial);
+	*(__le64 *)&ctx->buf[MD5_BLOCK_SIZE - 8] = cpu_to_le64(bitcount);
+	md5_blocks(&ctx->state, ctx->buf, 1);
+
+	cpu_to_le32_array(ctx->state.h, ARRAY_SIZE(ctx->state.h));
+	memcpy(out, ctx->state.h, MD5_DIGEST_SIZE);
+}
+
+void md5_final(struct md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE])
+{
+	__md5_final(ctx, out);
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+EXPORT_SYMBOL_GPL(md5_final);
+
+void md5(const u8 *data, size_t len, u8 out[MD5_DIGEST_SIZE])
+{
+	struct md5_ctx ctx;
+
+	md5_init(&ctx);
+	md5_update(&ctx, data, len);
+	md5_final(&ctx, out);
+}
+EXPORT_SYMBOL_GPL(md5);
+
+static void __hmac_md5_preparekey(struct md5_block_state *istate,
+				  struct md5_block_state *ostate,
+				  const u8 *raw_key, size_t raw_key_len)
+{
+	union {
+		u8 b[MD5_BLOCK_SIZE];
+		unsigned long w[MD5_BLOCK_SIZE / sizeof(unsigned long)];
+	} derived_key = { 0 };
+
+	if (unlikely(raw_key_len > MD5_BLOCK_SIZE))
+		md5(raw_key, raw_key_len, derived_key.b);
+	else
+		memcpy(derived_key.b, raw_key, raw_key_len);
+
+	for (size_t i = 0; i < ARRAY_SIZE(derived_key.w); i++)
+		derived_key.w[i] ^= REPEAT_BYTE(HMAC_IPAD_VALUE);
+	*istate = md5_iv;
+	md5_blocks(istate, derived_key.b, 1);
+
+	for (size_t i = 0; i < ARRAY_SIZE(derived_key.w); i++)
+		derived_key.w[i] ^= REPEAT_BYTE(HMAC_OPAD_VALUE ^
+						HMAC_IPAD_VALUE);
+	*ostate = md5_iv;
+	md5_blocks(ostate, derived_key.b, 1);
+
+	memzero_explicit(&derived_key, sizeof(derived_key));
+}
+
+void hmac_md5_preparekey(struct hmac_md5_key *key,
+			 const u8 *raw_key, size_t raw_key_len)
+{
+	__hmac_md5_preparekey(&key->istate, &key->ostate, raw_key, raw_key_len);
+}
+EXPORT_SYMBOL_GPL(hmac_md5_preparekey);
+
+void hmac_md5_init(struct hmac_md5_ctx *ctx, const struct hmac_md5_key *key)
+{
+	ctx->hash_ctx.state = key->istate;
+	ctx->hash_ctx.bytecount = MD5_BLOCK_SIZE;
+	ctx->ostate = key->ostate;
+}
+EXPORT_SYMBOL_GPL(hmac_md5_init);
+
+void hmac_md5_init_usingrawkey(struct hmac_md5_ctx *ctx,
+			       const u8 *raw_key, size_t raw_key_len)
+{
+	__hmac_md5_preparekey(&ctx->hash_ctx.state, &ctx->ostate,
+			      raw_key, raw_key_len);
+	ctx->hash_ctx.bytecount = MD5_BLOCK_SIZE;
+}
+EXPORT_SYMBOL_GPL(hmac_md5_init_usingrawkey);
+
+void hmac_md5_final(struct hmac_md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE])
+{
+	/* Generate the padded input for the outer hash in ctx->hash_ctx.buf. */
+	__md5_final(&ctx->hash_ctx, ctx->hash_ctx.buf);
+	memset(&ctx->hash_ctx.buf[MD5_DIGEST_SIZE], 0,
+	       MD5_BLOCK_SIZE - MD5_DIGEST_SIZE);
+	ctx->hash_ctx.buf[MD5_DIGEST_SIZE] = 0x80;
+	*(__le64 *)&ctx->hash_ctx.buf[MD5_BLOCK_SIZE - 8] =
+		cpu_to_le64(8 * (MD5_BLOCK_SIZE + MD5_DIGEST_SIZE));
+
+	/* Compute the outer hash, which gives the HMAC value. */
+	md5_blocks(&ctx->ostate, ctx->hash_ctx.buf, 1);
+	cpu_to_le32_array(ctx->ostate.h, ARRAY_SIZE(ctx->ostate.h));
+	memcpy(out, ctx->ostate.h, MD5_DIGEST_SIZE);
+
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+EXPORT_SYMBOL_GPL(hmac_md5_final);
+
+void hmac_md5(const struct hmac_md5_key *key,
+	      const u8 *data, size_t data_len, u8 out[MD5_DIGEST_SIZE])
+{
+	struct hmac_md5_ctx ctx;
+
+	hmac_md5_init(&ctx, key);
+	hmac_md5_update(&ctx, data, data_len);
+	hmac_md5_final(&ctx, out);
+}
+EXPORT_SYMBOL_GPL(hmac_md5);
+
+void hmac_md5_usingrawkey(const u8 *raw_key, size_t raw_key_len,
+			  const u8 *data, size_t data_len,
+			  u8 out[MD5_DIGEST_SIZE])
+{
+	struct hmac_md5_ctx ctx;
+
+	hmac_md5_init_usingrawkey(&ctx, raw_key, raw_key_len);
+	hmac_md5_update(&ctx, data, data_len);
+	hmac_md5_final(&ctx, out);
+}
+EXPORT_SYMBOL_GPL(hmac_md5_usingrawkey);
+
+MODULE_DESCRIPTION("MD5 and HMAC-MD5 library functions");
+MODULE_LICENSE("GPL");