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, 201 insertions, 0 deletions

diff --git a/crypto/mldsa.c b/crypto/mldsa.c
new file mode 100644
index 000000000..d8de082cc
--- /dev/null
+++ b/crypto/mldsa.c
@@ -0,0 +1,201 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * crypto_sig wrapper around ML-DSA library.
+ */
+#include <linux/init.h>
+#include <linux/module.h>
+#include <crypto/internal/sig.h>
+#include <crypto/mldsa.h>
+
+struct crypto_mldsa_ctx {
+	u8 pk[MAX(MAX(MLDSA44_PUBLIC_KEY_SIZE,
+		      MLDSA65_PUBLIC_KEY_SIZE),
+		  MLDSA87_PUBLIC_KEY_SIZE)];
+	unsigned int pk_len;
+	enum mldsa_alg strength;
+	bool key_set;
+};
+
+static int crypto_mldsa_sign(struct crypto_sig *tfm,
+			     const void *msg, unsigned int msg_len,
+			     void *sig, unsigned int sig_len)
+{
+	return -EOPNOTSUPP;
+}
+
+static int crypto_mldsa_verify(struct crypto_sig *tfm,
+			       const void *sig, unsigned int sig_len,
+			       const void *msg, unsigned int msg_len)
+{
+	const struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	if (unlikely(!ctx->key_set))
+		return -EINVAL;
+
+	return mldsa_verify(ctx->strength, sig, sig_len, msg, msg_len,
+			    ctx->pk, ctx->pk_len);
+}
+
+static unsigned int crypto_mldsa_key_size(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	switch (ctx->strength) {
+	case MLDSA44:
+		return MLDSA44_PUBLIC_KEY_SIZE;
+	case MLDSA65:
+		return MLDSA65_PUBLIC_KEY_SIZE;
+	case MLDSA87:
+		return MLDSA87_PUBLIC_KEY_SIZE;
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+}
+
+static int crypto_mldsa_set_pub_key(struct crypto_sig *tfm,
+				    const void *key, unsigned int keylen)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+	unsigned int expected_len = crypto_mldsa_key_size(tfm);
+
+	if (keylen != expected_len)
+		return -EINVAL;
+
+	ctx->pk_len = keylen;
+	memcpy(ctx->pk, key, keylen);
+	ctx->key_set = true;
+	return 0;
+}
+
+static int crypto_mldsa_set_priv_key(struct crypto_sig *tfm,
+				     const void *key, unsigned int keylen)
+{
+	return -EOPNOTSUPP;
+}
+
+static unsigned int crypto_mldsa_max_size(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	switch (ctx->strength) {
+	case MLDSA44:
+		return MLDSA44_SIGNATURE_SIZE;
+	case MLDSA65:
+		return MLDSA65_SIGNATURE_SIZE;
+	case MLDSA87:
+		return MLDSA87_SIGNATURE_SIZE;
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+}
+
+static int crypto_mldsa44_alg_init(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	ctx->strength = MLDSA44;
+	ctx->key_set = false;
+	return 0;
+}
+
+static int crypto_mldsa65_alg_init(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	ctx->strength = MLDSA65;
+	ctx->key_set = false;
+	return 0;
+}
+
+static int crypto_mldsa87_alg_init(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	ctx->strength = MLDSA87;
+	ctx->key_set = false;
+	return 0;
+}
+
+static void crypto_mldsa_alg_exit(struct crypto_sig *tfm)
+{
+}
+
+static struct sig_alg crypto_mldsa_algs[] = {
+	{
+		.sign			= crypto_mldsa_sign,
+		.verify			= crypto_mldsa_verify,
+		.set_pub_key		= crypto_mldsa_set_pub_key,
+		.set_priv_key		= crypto_mldsa_set_priv_key,
+		.key_size		= crypto_mldsa_key_size,
+		.max_size		= crypto_mldsa_max_size,
+		.init			= crypto_mldsa44_alg_init,
+		.exit			= crypto_mldsa_alg_exit,
+		.base.cra_name		= "mldsa44",
+		.base.cra_driver_name	= "mldsa44-lib",
+		.base.cra_ctxsize	= sizeof(struct crypto_mldsa_ctx),
+		.base.cra_module	= THIS_MODULE,
+		.base.cra_priority	= 5000,
+	}, {
+		.sign			= crypto_mldsa_sign,
+		.verify			= crypto_mldsa_verify,
+		.set_pub_key		= crypto_mldsa_set_pub_key,
+		.set_priv_key		= crypto_mldsa_set_priv_key,
+		.key_size		= crypto_mldsa_key_size,
+		.max_size		= crypto_mldsa_max_size,
+		.init			= crypto_mldsa65_alg_init,
+		.exit			= crypto_mldsa_alg_exit,
+		.base.cra_name		= "mldsa65",
+		.base.cra_driver_name	= "mldsa65-lib",
+		.base.cra_ctxsize	= sizeof(struct crypto_mldsa_ctx),
+		.base.cra_module	= THIS_MODULE,
+		.base.cra_priority	= 5000,
+	}, {
+		.sign			= crypto_mldsa_sign,
+		.verify			= crypto_mldsa_verify,
+		.set_pub_key		= crypto_mldsa_set_pub_key,
+		.set_priv_key		= crypto_mldsa_set_priv_key,
+		.key_size		= crypto_mldsa_key_size,
+		.max_size		= crypto_mldsa_max_size,
+		.init			= crypto_mldsa87_alg_init,
+		.exit			= crypto_mldsa_alg_exit,
+		.base.cra_name		= "mldsa87",
+		.base.cra_driver_name	= "mldsa87-lib",
+		.base.cra_ctxsize	= sizeof(struct crypto_mldsa_ctx),
+		.base.cra_module	= THIS_MODULE,
+		.base.cra_priority	= 5000,
+	},
+};
+
+static int __init mldsa_init(void)
+{
+	int ret, i;
+
+	for (i = 0; i < ARRAY_SIZE(crypto_mldsa_algs); i++) {
+		ret = crypto_register_sig(&crypto_mldsa_algs[i]);
+		if (ret < 0)
+			goto error;
+	}
+	return 0;
+
+error:
+	pr_err("Failed to register (%d)\n", ret);
+	for (i--; i >= 0; i--)
+		crypto_unregister_sig(&crypto_mldsa_algs[i]);
+	return ret;
+}
+module_init(mldsa_init);
+
+static void mldsa_exit(void)
+{
+	for (int i = 0; i < ARRAY_SIZE(crypto_mldsa_algs); i++)
+		crypto_unregister_sig(&crypto_mldsa_algs[i]);
+}
+module_exit(mldsa_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Crypto API support for ML-DSA signature verification");
+MODULE_ALIAS_CRYPTO("mldsa44");
+MODULE_ALIAS_CRYPTO("mldsa65");
+MODULE_ALIAS_CRYPTO("mldsa87");