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, 284 insertions, 0 deletions

diff --git a/include/net/mld.h b/include/net/mld.h
new file mode 100644
index 000000000..23255cc47
--- /dev/null
+++ b/include/net/mld.h
@@ -0,0 +1,284 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef LINUX_MLD_H
+#define LINUX_MLD_H
+
+#include <linux/in6.h>
+#include <linux/icmpv6.h>
+
+/* MLDv1 Query/Report/Done */
+struct mld_msg {
+	struct icmp6hdr		mld_hdr;
+	struct in6_addr		mld_mca;
+};
+
+#define mld_type		mld_hdr.icmp6_type
+#define mld_code		mld_hdr.icmp6_code
+#define mld_cksum		mld_hdr.icmp6_cksum
+#define mld_maxdelay		mld_hdr.icmp6_maxdelay
+#define mld_reserved		mld_hdr.icmp6_dataun.un_data16[1]
+
+/* Multicast Listener Discovery version 2 headers */
+/* MLDv2 Report */
+struct mld2_grec {
+	__u8		grec_type;
+	__u8		grec_auxwords;
+	__be16		grec_nsrcs;
+	struct in6_addr	grec_mca;
+	struct in6_addr	grec_src[];
+};
+
+struct mld2_report {
+	struct icmp6hdr		mld2r_hdr;
+	struct mld2_grec	mld2r_grec[];
+};
+
+#define mld2r_type		mld2r_hdr.icmp6_type
+#define mld2r_resv1		mld2r_hdr.icmp6_code
+#define mld2r_cksum		mld2r_hdr.icmp6_cksum
+#define mld2r_resv2		mld2r_hdr.icmp6_dataun.un_data16[0]
+#define mld2r_ngrec		mld2r_hdr.icmp6_dataun.un_data16[1]
+
+/* MLDv2 Query */
+struct mld2_query {
+	struct icmp6hdr		mld2q_hdr;
+	struct in6_addr		mld2q_mca;
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+	__u8			mld2q_qrv:3,
+				mld2q_suppress:1,
+				mld2q_resv2:4;
+#elif defined(__BIG_ENDIAN_BITFIELD)
+	__u8			mld2q_resv2:4,
+				mld2q_suppress:1,
+				mld2q_qrv:3;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+	__u8			mld2q_qqic;
+	__be16			mld2q_nsrcs;
+	struct in6_addr		mld2q_srcs[];
+};
+
+#define mld2q_type		mld2q_hdr.icmp6_type
+#define mld2q_code		mld2q_hdr.icmp6_code
+#define mld2q_cksum		mld2q_hdr.icmp6_cksum
+#define mld2q_mrc		mld2q_hdr.icmp6_maxdelay
+#define mld2q_resv1		mld2q_hdr.icmp6_dataun.un_data16[1]
+
+/* RFC3810, 5.1.3. Maximum Response Code:
+ *
+ * If Maximum Response Code >= 32768, Maximum Response Code represents a
+ * floating-point value as follows:
+ *
+ *  0 1 2 3 4 5 6 7 8 9 A B C D E F
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |1| exp |          mant         |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ */
+#define MLDV2_MRC_EXP(value)	(((value) >> 12) & 0x0007)
+#define MLDV2_MRC_MAN(value)	((value) & 0x0fff)
+
+/* RFC3810, 5.1.9. QQIC (Querier's Query Interval Code):
+ *
+ * If QQIC >= 128, QQIC represents a floating-point value as follows:
+ *
+ *  0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+
+ * |1| exp | mant  |
+ * +-+-+-+-+-+-+-+-+
+ */
+#define MLDV2_QQIC_EXP(value)	(((value) >> 4) & 0x07)
+#define MLDV2_QQIC_MAN(value)	((value) & 0x0f)
+
+/* MLDv2 QQIC floating-point exponential field min threshold */
+#define MLD_QQIC_MIN_THRESHOLD	128
+/* MLDv2 QQIC FP max threshold (mant = 0xF, exp = 7) -> 31744 */
+#define MLD_QQIC_MAX_THRESHOLD	31744
+/* MLDv2 MRC floating-point exponential field min threshold */
+#define MLD_MRC_MIN_THRESHOLD	32768UL
+/* MLDv2 MRC FP max threshold (mant = 0xFFF, exp = 7) -> 8387584 */
+#define MLD_MRC_MAX_THRESHOLD	8387584
+#define MLDV1_MRD_MAX_COMPAT	(MLD_MRC_MIN_THRESHOLD - 1)
+
+#define MLD_MAX_QUEUE		8
+#define MLD_MAX_SKBS		32
+
+/* V2 exponential field encoding */
+
+/*
+ * Calculate Maximum Response Code from Maximum Response Delay
+ *
+ * MRC represents the 16-bit encoded form of Maximum Response Delay (MRD);
+ * once decoded, the resulting value is in milliseconds.
+ *
+ * RFC3810, 5.1.3. defines only the decoding formula:
+ *     Maximum Response Delay = (mant | 0x1000) << (exp + 3)
+ *
+ * but does NOT define the encoding procedure. To derive exponent:
+ *
+ * For the 16-bit MRC, the "hidden bit" (0x1000) is left shifted by 12 to
+ * sit above the 12-bit mantissa. The RFC then shifts this entire block
+ * left by (exp + 3) to reconstruct the value. So, 'hidden bit' is the
+ * MSB which is shifted by (12 + exp + 3).
+ *
+ * Total left shift of the hidden bit = 12 + (exp + 3) = exp + 15.
+ * This is the MSB at the 0-based bit position: (exp + 15).
+ * Since fls() is 1-based, fls(value) - 1 = exp + 15.
+ *
+ * Therefore:
+ *     exp  = fls(value) - 16
+ *     mant = (value >> (exp + 3)) & 0x0FFF
+ *
+ * Final encoding formula:
+ *     0x8000 | (exp << 12) | mant
+ *
+ * Example (value = 1311744):
+ *  0               1               2               3
+ *  0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0| 1311744
+ * |                      ^-^--------mant---------^ ^...(exp+3)...^| exp=5
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * Encoded:
+ *   0x8000 | (5 << 12) | 0x404 = 0xD404
+ */
+static inline u16 mldv2_mrc(unsigned long mrd)
+{
+	u16 mc_man, mc_exp;
+
+	/* MRC < 32768 is literal */
+	if (mrd < MLD_MRC_MIN_THRESHOLD)
+		return mrd;
+
+	/* Saturate at max representable (mant = 0xFFF, exp = 7) -> 8387584 */
+	if (mrd >= MLD_MRC_MAX_THRESHOLD)
+		return 0xFFFF;
+
+	mc_exp = fls(mrd) - 16;
+	mc_man = (mrd >> (mc_exp + 3)) & 0x0FFF;
+
+	return 0x8000 | (mc_exp << 12) | mc_man;
+}
+
+/*
+ * Calculate Querier's Query Interval Code from Querier's Query Interval
+ *
+ * QQIC represents the 8-bit encoded form of Querier's Query Interval (QQI);
+ * once decoded, the resulting value is in seconds.
+ *
+ * RFC3810, 5.1.9. defines only the decoding formula:
+ *     QQI = (mant | 0x10) << (exp + 3)
+ *
+ * but does NOT define the encoding procedure. To derive exponent:
+ *
+ * For any value of mantissa and exponent, the decoding formula indicates
+ * that the "hidden bit" (0x10) is shifted 4 bits left to sit above the
+ * 4-bit mantissa. The RFC again shifts this entire block left by (exp + 3)
+ * to reconstruct the value. So, 'hidden bit' is the MSB which is shifted
+ * by (4 + exp + 3).
+ *
+ * Total left shift of the 'hidden bit' = 4 + (exp + 3) = exp + 7.
+ * This is the MSB at the 0-based bit position: (exp + 7).
+ * Since fls() is 1-based, fls(value) - 1 = exp + 7.
+ *
+ * Therefore:
+ *     exp  = fls(value) - 8
+ *     mant = (value >> (exp + 3)) & 0x0F
+ *
+ * Final encoding formula:
+ *     0x80 | (exp << 4) | mant
+ *
+ * Example (value = 3200):
+ *  0               1
+ *  0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0| (value = 3200)
+ * |        ^-^-mant^ ^..(exp+3)..^| exp = 4, mant = 9
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * Encoded:
+ *   0x80 | (4 << 4) | 9 = 0xC9
+ */
+static inline u8 mldv2_qqic(unsigned long value)
+{
+	u8 mc_man, mc_exp;
+
+	/* QQIC < 128 is literal */
+	if (value < MLD_QQIC_MIN_THRESHOLD)
+		return value;
+
+	/* Saturate at max representable (mant = 0xF, exp = 7) -> 31744 */
+	if (value >= MLD_QQIC_MAX_THRESHOLD)
+		return 0xFF;
+
+	mc_exp  = fls(value) - 8;
+	mc_man = (value >> (mc_exp + 3)) & 0x0F;
+
+	return 0x80 | (mc_exp << 4) | mc_man;
+}
+
+/* V2 exponential field decoding */
+
+/* Calculate Maximum Response Delay from Maximum Response Code
+ *
+ * RFC3810, relevant sections:
+ *  - 5.1.3. Maximum Response Code defines the decoding formula:
+ *      0 1 2 3 4 5 6 7 8 9 A B C D E F
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |1| exp |          mant         |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *    Maximum Response Delay = (mant | 0x1000) << (exp+3)
+ *  - 9.3. Query Response Interval
+ *
+ * After decode, MRC represents the Maximum Response Delay (MRD) in
+ * units of milliseconds.
+ */
+static inline unsigned long mldv2_mrd(const struct mld2_query *mlh2)
+{
+	unsigned long mc_mrc = ntohs(mlh2->mld2q_mrc);
+
+	if (mc_mrc < MLD_MRC_MIN_THRESHOLD) {
+		return mc_mrc;
+	} else {
+		unsigned long mc_man, mc_exp;
+
+		mc_exp = MLDV2_MRC_EXP(mc_mrc);
+		mc_man = MLDV2_MRC_MAN(mc_mrc);
+
+		return (mc_man | 0x1000) << (mc_exp + 3);
+	}
+}
+
+/* Calculate Querier's Query Interval from Querier's Query Interval Code
+ *
+ * RFC3810, relevant sections:
+ *  - 5.1.9. QQIC (Querier's Query Interval Code) defines the decoding formula:
+ *      0 1 2 3 4 5 6 7
+ *     +-+-+-+-+-+-+-+-+
+ *     |1| exp | mant  |
+ *     +-+-+-+-+-+-+-+-+
+ *    QQI = (mant | 0x10) << (exp + 3)
+ *  - 9.2. Query Interval
+ *  - 9.12. Older Version Querier Present Timeout
+ *    (the [Query Interval] in the last Query received)
+ *
+ * After decode, QQIC represents the Querier's Query Interval in units
+ * of seconds.
+ */
+static inline unsigned long mldv2_qqi(const struct mld2_query *mlh2)
+{
+	unsigned long qqic = mlh2->mld2q_qqic;
+
+	if (qqic < MLD_QQIC_MIN_THRESHOLD) {
+		return qqic;
+	} else {
+		unsigned long mc_man, mc_exp;
+
+		mc_exp = MLDV2_QQIC_EXP(qqic);
+		mc_man = MLDV2_QQIC_MAN(qqic);
+
+		return (mc_man | 0x10) << (mc_exp + 3);
+	}
+}
+
+#endif