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, 170 insertions, 0 deletions

diff --git a/lib/crypto/blake2b.c b/lib/crypto/blake2b.c
new file mode 100644
index 000000000..581b7f848
--- /dev/null
+++ b/lib/crypto/blake2b.c
@@ -0,0 +1,170 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+/*
+ * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ * Copyright 2025 Google LLC
+ *
+ * This is an implementation of the BLAKE2b hash and PRF functions.
+ *
+ * Information: https://blake2.net/
+ */
+
+#include <crypto/blake2b.h>
+#include <linux/bug.h>
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/unroll.h>
+#include <linux/types.h>
+
+static const u8 blake2b_sigma[12][16] = {
+	{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 },
+	{ 14, 10, 4, 8, 9, 15, 13, 6, 1, 12, 0, 2, 11, 7, 5, 3 },
+	{ 11, 8, 12, 0, 5, 2, 15, 13, 10, 14, 3, 6, 7, 1, 9, 4 },
+	{ 7, 9, 3, 1, 13, 12, 11, 14, 2, 6, 5, 10, 4, 0, 15, 8 },
+	{ 9, 0, 5, 7, 2, 4, 10, 15, 14, 1, 11, 12, 6, 8, 3, 13 },
+	{ 2, 12, 6, 10, 0, 11, 8, 3, 4, 13, 7, 5, 15, 14, 1, 9 },
+	{ 12, 5, 1, 15, 14, 13, 4, 10, 0, 7, 6, 3, 9, 2, 8, 11 },
+	{ 13, 11, 7, 14, 12, 1, 3, 9, 5, 0, 15, 4, 8, 6, 2, 10 },
+	{ 6, 15, 14, 9, 11, 3, 0, 8, 12, 2, 13, 7, 1, 4, 10, 5 },
+	{ 10, 2, 8, 4, 7, 6, 1, 5, 15, 11, 9, 14, 3, 12, 13, 0 },
+	{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 },
+	{ 14, 10, 4, 8, 9, 15, 13, 6, 1, 12, 0, 2, 11, 7, 5, 3 }
+};
+
+static inline void blake2b_increment_counter(struct blake2b_ctx *ctx, u32 inc)
+{
+	ctx->t[0] += inc;
+	ctx->t[1] += (ctx->t[0] < inc);
+}
+
+static void __maybe_unused
+blake2b_compress_generic(struct blake2b_ctx *ctx,
+			 const u8 *data, size_t nblocks, u32 inc)
+{
+	u64 m[16];
+	u64 v[16];
+	int i;
+
+	WARN_ON(IS_ENABLED(DEBUG) &&
+		(nblocks > 1 && inc != BLAKE2B_BLOCK_SIZE));
+
+	while (nblocks > 0) {
+		blake2b_increment_counter(ctx, inc);
+		memcpy(m, data, BLAKE2B_BLOCK_SIZE);
+		le64_to_cpu_array(m, ARRAY_SIZE(m));
+		memcpy(v, ctx->h, 64);
+		v[ 8] = BLAKE2B_IV0;
+		v[ 9] = BLAKE2B_IV1;
+		v[10] = BLAKE2B_IV2;
+		v[11] = BLAKE2B_IV3;
+		v[12] = BLAKE2B_IV4 ^ ctx->t[0];
+		v[13] = BLAKE2B_IV5 ^ ctx->t[1];
+		v[14] = BLAKE2B_IV6 ^ ctx->f[0];
+		v[15] = BLAKE2B_IV7 ^ ctx->f[1];
+
+#define G(r, i, a, b, c, d) do { \
+	a += b + m[blake2b_sigma[r][2 * i + 0]]; \
+	d = ror64(d ^ a, 32); \
+	c += d; \
+	b = ror64(b ^ c, 24); \
+	a += b + m[blake2b_sigma[r][2 * i + 1]]; \
+	d = ror64(d ^ a, 16); \
+	c += d; \
+	b = ror64(b ^ c, 63); \
+} while (0)
+
+#ifdef CONFIG_64BIT
+		/*
+		 * Unroll the rounds loop to enable constant-folding of the
+		 * blake2b_sigma values.  Seems worthwhile on 64-bit kernels.
+		 * Not worthwhile on 32-bit kernels because the code size is
+		 * already so large there due to BLAKE2b using 64-bit words.
+		 */
+		unrolled_full
+#endif
+		for (int r = 0; r < 12; r++) {
+			G(r, 0, v[0], v[4], v[8], v[12]);
+			G(r, 1, v[1], v[5], v[9], v[13]);
+			G(r, 2, v[2], v[6], v[10], v[14]);
+			G(r, 3, v[3], v[7], v[11], v[15]);
+			G(r, 4, v[0], v[5], v[10], v[15]);
+			G(r, 5, v[1], v[6], v[11], v[12]);
+			G(r, 6, v[2], v[7], v[8], v[13]);
+			G(r, 7, v[3], v[4], v[9], v[14]);
+		}
+#undef G
+
+		for (i = 0; i < 8; ++i)
+			ctx->h[i] ^= v[i] ^ v[i + 8];
+
+		data += BLAKE2B_BLOCK_SIZE;
+		--nblocks;
+	}
+}
+
+#ifdef CONFIG_CRYPTO_LIB_BLAKE2B_ARCH
+#include "blake2b.h" /* $(SRCARCH)/blake2b.h */
+#else
+#define blake2b_compress blake2b_compress_generic
+#endif
+
+static inline void blake2b_set_lastblock(struct blake2b_ctx *ctx)
+{
+	ctx->f[0] = -1;
+}
+
+void blake2b_update(struct blake2b_ctx *ctx, const u8 *in, size_t inlen)
+{
+	const size_t fill = BLAKE2B_BLOCK_SIZE - ctx->buflen;
+
+	if (unlikely(!inlen))
+		return;
+	if (inlen > fill) {
+		memcpy(ctx->buf + ctx->buflen, in, fill);
+		blake2b_compress(ctx, ctx->buf, 1, BLAKE2B_BLOCK_SIZE);
+		ctx->buflen = 0;
+		in += fill;
+		inlen -= fill;
+	}
+	if (inlen > BLAKE2B_BLOCK_SIZE) {
+		const size_t nblocks = DIV_ROUND_UP(inlen, BLAKE2B_BLOCK_SIZE);
+
+		blake2b_compress(ctx, in, nblocks - 1, BLAKE2B_BLOCK_SIZE);
+		in += BLAKE2B_BLOCK_SIZE * (nblocks - 1);
+		inlen -= BLAKE2B_BLOCK_SIZE * (nblocks - 1);
+	}
+	memcpy(ctx->buf + ctx->buflen, in, inlen);
+	ctx->buflen += inlen;
+}
+EXPORT_SYMBOL(blake2b_update);
+
+void blake2b_final(struct blake2b_ctx *ctx, u8 *out)
+{
+	WARN_ON(IS_ENABLED(DEBUG) && !out);
+	blake2b_set_lastblock(ctx);
+	memset(ctx->buf + ctx->buflen, 0,
+	       BLAKE2B_BLOCK_SIZE - ctx->buflen); /* Padding */
+	blake2b_compress(ctx, ctx->buf, 1, ctx->buflen);
+	cpu_to_le64_array(ctx->h, ARRAY_SIZE(ctx->h));
+	memcpy(out, ctx->h, ctx->outlen);
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+EXPORT_SYMBOL(blake2b_final);
+
+#ifdef blake2b_mod_init_arch
+static int __init blake2b_mod_init(void)
+{
+	blake2b_mod_init_arch();
+	return 0;
+}
+subsys_initcall(blake2b_mod_init);
+
+static void __exit blake2b_mod_exit(void)
+{
+}
+module_exit(blake2b_mod_exit);
+#endif
+
+MODULE_DESCRIPTION("BLAKE2b hash function");
+MODULE_LICENSE("GPL");