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, 317 insertions, 0 deletions

diff --git a/net/ipv4/tcp_htcp.c b/net/ipv4/tcp_htcp.c
new file mode 100644
index 000000000..81b96331b
--- /dev/null
+++ b/net/ipv4/tcp_htcp.c
@@ -0,0 +1,317 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * H-TCP congestion control. The algorithm is detailed in:
+ * R.N.Shorten, D.J.Leith:
+ *   "H-TCP: TCP for high-speed and long-distance networks"
+ *   Proc. PFLDnet, Argonne, 2004.
+ * https://www.hamilton.ie/net/htcp3.pdf
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <net/tcp.h>
+
+#define ALPHA_BASE	(1<<7)	/* 1.0 with shift << 7 */
+#define BETA_MIN	(1<<6)	/* 0.5 with shift << 7 */
+#define BETA_MAX	102	/* 0.8 with shift << 7 */
+
+static int use_rtt_scaling __read_mostly = 1;
+module_param(use_rtt_scaling, int, 0644);
+MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
+
+static int use_bandwidth_switch __read_mostly = 1;
+module_param(use_bandwidth_switch, int, 0644);
+MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
+
+struct htcp {
+	u32	alpha;		/* Fixed point arith, << 7 */
+	u8	beta;           /* Fixed point arith, << 7 */
+	u8	modeswitch;	/* Delay modeswitch
+				   until we had at least one congestion event */
+	u16	pkts_acked;
+	u32	packetcount;
+	u32	minRTT;
+	u32	maxRTT;
+	u32	last_cong;	/* Time since last congestion event end */
+	u32	undo_last_cong;
+
+	u32	undo_maxRTT;
+	u32	undo_old_maxB;
+
+	/* Bandwidth estimation */
+	u32	minB;
+	u32	maxB;
+	u32	old_maxB;
+	u32	Bi;
+	u32	lasttime;
+};
+
+static inline u32 htcp_cong_time(const struct htcp *ca)
+{
+	return jiffies - ca->last_cong;
+}
+
+static inline u32 htcp_ccount(const struct htcp *ca)
+{
+	return htcp_cong_time(ca) / ca->minRTT;
+}
+
+static inline void htcp_reset(struct htcp *ca)
+{
+	ca->undo_last_cong = ca->last_cong;
+	ca->undo_maxRTT = ca->maxRTT;
+	ca->undo_old_maxB = ca->old_maxB;
+
+	ca->last_cong = jiffies;
+}
+
+static u32 htcp_cwnd_undo(struct sock *sk)
+{
+	struct htcp *ca = inet_csk_ca(sk);
+
+	if (ca->undo_last_cong) {
+		ca->last_cong = ca->undo_last_cong;
+		ca->maxRTT = ca->undo_maxRTT;
+		ca->old_maxB = ca->undo_old_maxB;
+		ca->undo_last_cong = 0;
+	}
+
+	return tcp_reno_undo_cwnd(sk);
+}
+
+static inline void measure_rtt(struct sock *sk, u32 srtt)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	struct htcp *ca = inet_csk_ca(sk);
+
+	/* keep track of minimum RTT seen so far, minRTT is zero at first */
+	if (ca->minRTT > srtt || !ca->minRTT)
+		ca->minRTT = srtt;
+
+	/* max RTT */
+	if (icsk->icsk_ca_state == TCP_CA_Open) {
+		if (ca->maxRTT < ca->minRTT)
+			ca->maxRTT = ca->minRTT;
+		if (ca->maxRTT < srtt &&
+		    srtt <= ca->maxRTT + msecs_to_jiffies(20))
+			ca->maxRTT = srtt;
+	}
+}
+
+static void measure_achieved_throughput(struct sock *sk,
+					const struct ack_sample *sample)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	const struct tcp_sock *tp = tcp_sk(sk);
+	struct htcp *ca = inet_csk_ca(sk);
+	u32 now = tcp_jiffies32;
+
+	if (icsk->icsk_ca_state == TCP_CA_Open)
+		ca->pkts_acked = sample->pkts_acked;
+
+	if (sample->rtt_us > 0)
+		measure_rtt(sk, usecs_to_jiffies(sample->rtt_us));
+
+	if (!use_bandwidth_switch)
+		return;
+
+	/* achieved throughput calculations */
+	if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_Disorder))) {
+		ca->packetcount = 0;
+		ca->lasttime = now;
+		return;
+	}
+
+	ca->packetcount += sample->pkts_acked;
+
+	if (ca->packetcount >= tcp_snd_cwnd(tp) - (ca->alpha >> 7 ? : 1) &&
+	    now - ca->lasttime >= ca->minRTT &&
+	    ca->minRTT > 0) {
+		__u32 cur_Bi = ca->packetcount * HZ / (now - ca->lasttime);
+
+		if (htcp_ccount(ca) <= 3) {
+			/* just after backoff */
+			ca->minB = ca->maxB = ca->Bi = cur_Bi;
+		} else {
+			ca->Bi = (3 * ca->Bi + cur_Bi) / 4;
+			if (ca->Bi > ca->maxB)
+				ca->maxB = ca->Bi;
+			if (ca->minB > ca->maxB)
+				ca->minB = ca->maxB;
+		}
+		ca->packetcount = 0;
+		ca->lasttime = now;
+	}
+}
+
+static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)
+{
+	if (use_bandwidth_switch) {
+		u32 maxB = ca->maxB;
+		u32 old_maxB = ca->old_maxB;
+
+		ca->old_maxB = ca->maxB;
+		if (!between(5 * maxB, 4 * old_maxB, 6 * old_maxB)) {
+			ca->beta = BETA_MIN;
+			ca->modeswitch = 0;
+			return;
+		}
+	}
+
+	if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) {
+		ca->beta = (minRTT << 7) / maxRTT;
+		if (ca->beta < BETA_MIN)
+			ca->beta = BETA_MIN;
+		else if (ca->beta > BETA_MAX)
+			ca->beta = BETA_MAX;
+	} else {
+		ca->beta = BETA_MIN;
+		ca->modeswitch = 1;
+	}
+}
+
+static inline void htcp_alpha_update(struct htcp *ca)
+{
+	u32 minRTT = ca->minRTT;
+	u32 factor = 1;
+	u32 diff = htcp_cong_time(ca);
+
+	if (diff > HZ) {
+		diff -= HZ;
+		factor = 1 + (10 * diff + ((diff / 2) * (diff / 2) / HZ)) / HZ;
+	}
+
+	if (use_rtt_scaling && minRTT) {
+		u32 scale = (HZ << 3) / (10 * minRTT);
+
+		/* clamping ratio to interval [0.5,10]<<3 */
+		scale = clamp(scale, 1U << 2, 10U << 3);
+		factor = (factor << 3) / scale;
+		if (!factor)
+			factor = 1;
+	}
+
+	ca->alpha = 2 * factor * ((1 << 7) - ca->beta);
+	if (!ca->alpha)
+		ca->alpha = ALPHA_BASE;
+}
+
+/*
+ * After we have the rtt data to calculate beta, we'd still prefer to wait one
+ * rtt before we adjust our beta to ensure we are working from a consistent
+ * data.
+ *
+ * This function should be called when we hit a congestion event since only at
+ * that point do we really have a real sense of maxRTT (the queues en route
+ * were getting just too full now).
+ */
+static void htcp_param_update(struct sock *sk)
+{
+	struct htcp *ca = inet_csk_ca(sk);
+	u32 minRTT = ca->minRTT;
+	u32 maxRTT = ca->maxRTT;
+
+	htcp_beta_update(ca, minRTT, maxRTT);
+	htcp_alpha_update(ca);
+
+	/* add slowly fading memory for maxRTT to accommodate routing changes */
+	if (minRTT > 0 && maxRTT > minRTT)
+		ca->maxRTT = minRTT + ((maxRTT - minRTT) * 95) / 100;
+}
+
+static u32 htcp_recalc_ssthresh(struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	const struct htcp *ca = inet_csk_ca(sk);
+
+	htcp_param_update(sk);
+	return max((tcp_snd_cwnd(tp) * ca->beta) >> 7, 2U);
+}
+
+static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct htcp *ca = inet_csk_ca(sk);
+
+	if (!tcp_is_cwnd_limited(sk))
+		return;
+
+	if (tcp_in_slow_start(tp))
+		tcp_slow_start(tp, acked);
+	else {
+		/* In dangerous area, increase slowly.
+		 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
+		 */
+		if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tcp_snd_cwnd(tp)) {
+			if (tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp)
+				tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
+			tp->snd_cwnd_cnt = 0;
+			htcp_alpha_update(ca);
+		} else
+			tp->snd_cwnd_cnt += ca->pkts_acked;
+
+		ca->pkts_acked = 1;
+	}
+}
+
+static void htcp_init(struct sock *sk)
+{
+	struct htcp *ca = inet_csk_ca(sk);
+
+	memset(ca, 0, sizeof(struct htcp));
+	ca->alpha = ALPHA_BASE;
+	ca->beta = BETA_MIN;
+	ca->pkts_acked = 1;
+	ca->last_cong = jiffies;
+}
+
+static void htcp_state(struct sock *sk, u8 new_state)
+{
+	switch (new_state) {
+	case TCP_CA_Open:
+		{
+			struct htcp *ca = inet_csk_ca(sk);
+
+			if (ca->undo_last_cong) {
+				ca->last_cong = jiffies;
+				ca->undo_last_cong = 0;
+			}
+		}
+		break;
+	case TCP_CA_CWR:
+	case TCP_CA_Recovery:
+	case TCP_CA_Loss:
+		htcp_reset(inet_csk_ca(sk));
+		break;
+	}
+}
+
+static struct tcp_congestion_ops htcp __read_mostly = {
+	.init		= htcp_init,
+	.ssthresh	= htcp_recalc_ssthresh,
+	.cong_avoid	= htcp_cong_avoid,
+	.set_state	= htcp_state,
+	.undo_cwnd	= htcp_cwnd_undo,
+	.pkts_acked	= measure_achieved_throughput,
+	.owner		= THIS_MODULE,
+	.name		= "htcp",
+};
+
+static int __init htcp_register(void)
+{
+	BUILD_BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
+	BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
+	return tcp_register_congestion_control(&htcp);
+}
+
+static void __exit htcp_unregister(void)
+{
+	tcp_unregister_congestion_control(&htcp);
+}
+
+module_init(htcp_register);
+module_exit(htcp_unregister);
+
+MODULE_AUTHOR("Baruch Even");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("H-TCP");