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, 158 insertions, 0 deletions

diff --git a/lib/crypto/x86/poly1305.h b/lib/crypto/x86/poly1305.h
new file mode 100644
index 000000000..ee92e3740
--- /dev/null
+++ b/lib/crypto/x86/poly1305.h
@@ -0,0 +1,158 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+/*
+ * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#include <asm/cpu_device_id.h>
+#include <asm/fpu/api.h>
+#include <linux/jump_label.h>
+#include <linux/kernel.h>
+#include <linux/sizes.h>
+
+struct poly1305_arch_internal {
+	union {
+		struct {
+			u32 h[5];
+			u32 is_base2_26;
+		};
+		u64 hs[3];
+	};
+	u64 r[2];
+	u64 pad;
+	struct { u32 r2, r1, r4, r3; } rn[9];
+};
+
+/*
+ * The AVX code uses base 2^26, while the scalar code uses base 2^64. If we hit
+ * the unfortunate situation of using AVX and then having to go back to scalar
+ * -- because the user is silly and has called the update function from two
+ * separate contexts -- then we need to convert back to the original base before
+ * proceeding. It is possible to reason that the initial reduction below is
+ * sufficient given the implementation invariants. However, for an avoidance of
+ * doubt and because this is not performance critical, we do the full reduction
+ * anyway. Z3 proof of below function: https://xn--4db.cc/ltPtHCKN/py
+ */
+static void convert_to_base2_64(void *ctx)
+{
+	struct poly1305_arch_internal *state = ctx;
+	u32 cy;
+
+	if (!state->is_base2_26)
+		return;
+
+	cy = state->h[0] >> 26; state->h[0] &= 0x3ffffff; state->h[1] += cy;
+	cy = state->h[1] >> 26; state->h[1] &= 0x3ffffff; state->h[2] += cy;
+	cy = state->h[2] >> 26; state->h[2] &= 0x3ffffff; state->h[3] += cy;
+	cy = state->h[3] >> 26; state->h[3] &= 0x3ffffff; state->h[4] += cy;
+	state->hs[0] = ((u64)state->h[2] << 52) | ((u64)state->h[1] << 26) | state->h[0];
+	state->hs[1] = ((u64)state->h[4] << 40) | ((u64)state->h[3] << 14) | (state->h[2] >> 12);
+	state->hs[2] = state->h[4] >> 24;
+	/* Unsigned Less Than: branchlessly produces 1 if a < b, else 0. */
+#define ULT(a, b) ((a ^ ((a ^ b) | ((a - b) ^ b))) >> (sizeof(a) * 8 - 1))
+	cy = (state->hs[2] >> 2) + (state->hs[2] & ~3ULL);
+	state->hs[2] &= 3;
+	state->hs[0] += cy;
+	state->hs[1] += (cy = ULT(state->hs[0], cy));
+	state->hs[2] += ULT(state->hs[1], cy);
+#undef ULT
+	state->is_base2_26 = 0;
+}
+
+asmlinkage void poly1305_init_x86_64(struct poly1305_block_state *state,
+				     const u8 raw_key[POLY1305_BLOCK_SIZE]);
+asmlinkage void poly1305_blocks_x86_64(struct poly1305_arch_internal *ctx,
+				       const u8 *inp,
+				       const size_t len, const u32 padbit);
+asmlinkage void poly1305_emit_x86_64(const struct poly1305_state *ctx,
+				     u8 mac[POLY1305_DIGEST_SIZE],
+				     const u32 nonce[4]);
+asmlinkage void poly1305_emit_avx(const struct poly1305_state *ctx,
+				  u8 mac[POLY1305_DIGEST_SIZE],
+				  const u32 nonce[4]);
+asmlinkage void poly1305_blocks_avx(struct poly1305_arch_internal *ctx,
+				    const u8 *inp, const size_t len,
+				    const u32 padbit);
+asmlinkage void poly1305_blocks_avx2(struct poly1305_arch_internal *ctx,
+				     const u8 *inp, const size_t len,
+				     const u32 padbit);
+asmlinkage void poly1305_blocks_avx512(struct poly1305_arch_internal *ctx,
+				       const u8 *inp,
+				       const size_t len, const u32 padbit);
+
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(poly1305_use_avx);
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(poly1305_use_avx2);
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(poly1305_use_avx512);
+
+static void poly1305_block_init(struct poly1305_block_state *state,
+				const u8 raw_key[POLY1305_BLOCK_SIZE])
+{
+	poly1305_init_x86_64(state, raw_key);
+}
+
+static void poly1305_blocks(struct poly1305_block_state *state, const u8 *inp,
+			    unsigned int len, u32 padbit)
+{
+	struct poly1305_arch_internal *ctx =
+		container_of(&state->h.h, struct poly1305_arch_internal, h);
+
+	/* SIMD disables preemption, so relax after processing each page. */
+	BUILD_BUG_ON(SZ_4K < POLY1305_BLOCK_SIZE ||
+		     SZ_4K % POLY1305_BLOCK_SIZE);
+
+	/*
+	 * The AVX implementations have significant setup overhead (e.g. key
+	 * power computation, kernel FPU enabling) which makes them slower for
+	 * short messages.  Fall back to the scalar implementation for messages
+	 * shorter than 288 bytes, unless the AVX-specific key setup has already
+	 * been performed (indicated by ctx->is_base2_26).
+	 */
+	if (!static_branch_likely(&poly1305_use_avx) ||
+	    (len < POLY1305_BLOCK_SIZE * 18 && !ctx->is_base2_26) ||
+	    unlikely(!irq_fpu_usable())) {
+		convert_to_base2_64(ctx);
+		poly1305_blocks_x86_64(ctx, inp, len, padbit);
+		return;
+	}
+
+	do {
+		const unsigned int bytes = min(len, SZ_4K);
+
+		kernel_fpu_begin();
+		if (static_branch_likely(&poly1305_use_avx512))
+			poly1305_blocks_avx512(ctx, inp, bytes, padbit);
+		else if (static_branch_likely(&poly1305_use_avx2))
+			poly1305_blocks_avx2(ctx, inp, bytes, padbit);
+		else
+			poly1305_blocks_avx(ctx, inp, bytes, padbit);
+		kernel_fpu_end();
+
+		len -= bytes;
+		inp += bytes;
+	} while (len);
+}
+
+static void poly1305_emit(const struct poly1305_state *ctx,
+			  u8 mac[POLY1305_DIGEST_SIZE], const u32 nonce[4])
+{
+	if (!static_branch_likely(&poly1305_use_avx))
+		poly1305_emit_x86_64(ctx, mac, nonce);
+	else
+		poly1305_emit_avx(ctx, mac, nonce);
+}
+
+#define poly1305_mod_init_arch poly1305_mod_init_arch
+static void poly1305_mod_init_arch(void)
+{
+	if (boot_cpu_has(X86_FEATURE_AVX) &&
+	    cpu_has_xfeatures(XFEATURE_MASK_SSE | XFEATURE_MASK_YMM, NULL))
+		static_branch_enable(&poly1305_use_avx);
+	if (boot_cpu_has(X86_FEATURE_AVX) && boot_cpu_has(X86_FEATURE_AVX2) &&
+	    cpu_has_xfeatures(XFEATURE_MASK_SSE | XFEATURE_MASK_YMM, NULL))
+		static_branch_enable(&poly1305_use_avx2);
+	if (boot_cpu_has(X86_FEATURE_AVX) && boot_cpu_has(X86_FEATURE_AVX2) &&
+	    boot_cpu_has(X86_FEATURE_AVX512F) &&
+	    cpu_has_xfeatures(XFEATURE_MASK_SSE | XFEATURE_MASK_YMM | XFEATURE_MASK_AVX512, NULL) &&
+	    /* Skylake downclocks unacceptably much when using zmm, but later generations are fast. */
+	    boot_cpu_data.x86_vfm != INTEL_SKYLAKE_X)
+		static_branch_enable(&poly1305_use_avx512);
+}