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, 102 insertions, 0 deletions

diff --git a/net/mac80211/eht.c b/net/mac80211/eht.c
new file mode 100644
index 000000000..23fe82df6
--- /dev/null
+++ b/net/mac80211/eht.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * EHT handling
+ *
+ * Copyright(c) 2021-2026 Intel Corporation
+ */
+
+#include "driver-ops.h"
+#include "ieee80211_i.h"
+
+void
+ieee80211_eht_cap_ie_to_sta_eht_cap(struct ieee80211_sub_if_data *sdata,
+				    struct ieee80211_supported_band *sband,
+				    const u8 *he_cap_ie, u8 he_cap_len,
+				    const struct ieee80211_eht_cap_elem *eht_cap_ie_elem,
+				    u8 eht_cap_len,
+				    struct link_sta_info *link_sta)
+{
+	struct ieee80211_sta_eht_cap *eht_cap = &link_sta->pub->eht_cap;
+	struct ieee80211_he_cap_elem *he_cap_ie_elem = (void *)he_cap_ie;
+	u8 eht_ppe_size = 0;
+	u8 mcs_nss_size;
+	u8 eht_total_size = sizeof(eht_cap->eht_cap_elem);
+	u8 *pos = (u8 *)eht_cap_ie_elem;
+
+	memset(eht_cap, 0, sizeof(*eht_cap));
+
+	if (!eht_cap_ie_elem ||
+	    !ieee80211_get_eht_iftype_cap_vif(sband, &sdata->vif))
+		return;
+
+	mcs_nss_size = ieee80211_eht_mcs_nss_size(he_cap_ie_elem,
+						  &eht_cap_ie_elem->fixed,
+						  sdata->vif.type ==
+							NL80211_IFTYPE_STATION);
+
+	eht_total_size += mcs_nss_size;
+
+	/* Calculate the PPE thresholds length only if the header is present */
+	if (eht_cap_ie_elem->fixed.phy_cap_info[5] &
+			IEEE80211_EHT_PHY_CAP5_PPE_THRESHOLD_PRESENT) {
+		u16 eht_ppe_hdr;
+
+		if (eht_cap_len < eht_total_size + sizeof(u16))
+			return;
+
+		eht_ppe_hdr = get_unaligned_le16(eht_cap_ie_elem->optional + mcs_nss_size);
+		eht_ppe_size =
+			ieee80211_eht_ppe_size(eht_ppe_hdr,
+					       eht_cap_ie_elem->fixed.phy_cap_info);
+		eht_total_size += eht_ppe_size;
+
+		/* we calculate as if NSS > 8 are valid, but don't handle that */
+		if (eht_ppe_size > sizeof(eht_cap->eht_ppe_thres))
+			return;
+	}
+
+	if (eht_cap_len < eht_total_size)
+		return;
+
+	/* Copy the static portion of the EHT capabilities */
+	memcpy(&eht_cap->eht_cap_elem, pos, sizeof(eht_cap->eht_cap_elem));
+	pos += sizeof(eht_cap->eht_cap_elem);
+
+	/* Copy MCS/NSS which depends on the peer capabilities */
+	memset(&eht_cap->eht_mcs_nss_supp, 0,
+	       sizeof(eht_cap->eht_mcs_nss_supp));
+	memcpy(&eht_cap->eht_mcs_nss_supp, pos, mcs_nss_size);
+
+	if (eht_ppe_size)
+		memcpy(eht_cap->eht_ppe_thres,
+		       &eht_cap_ie_elem->optional[mcs_nss_size],
+		       eht_ppe_size);
+
+	eht_cap->has_eht = true;
+
+	/*
+	 * The MPDU length bits are reserved on all but 2.4 GHz and get set via
+	 * VHT (5 GHz) or HE (6 GHz) capabilities.
+	 */
+	if (sband->band != NL80211_BAND_2GHZ)
+		return;
+
+	switch (u8_get_bits(eht_cap->eht_cap_elem.mac_cap_info[0],
+			    IEEE80211_EHT_MAC_CAP0_MAX_MPDU_LEN_MASK)) {
+	case IEEE80211_EHT_MAC_CAP0_MAX_MPDU_LEN_11454:
+		link_sta->pub->agg.max_amsdu_len =
+			IEEE80211_MAX_MPDU_LEN_VHT_11454;
+		break;
+	case IEEE80211_EHT_MAC_CAP0_MAX_MPDU_LEN_7991:
+		link_sta->pub->agg.max_amsdu_len =
+			IEEE80211_MAX_MPDU_LEN_VHT_7991;
+		break;
+	case IEEE80211_EHT_MAC_CAP0_MAX_MPDU_LEN_3895:
+	default:
+		link_sta->pub->agg.max_amsdu_len =
+			IEEE80211_MAX_MPDU_LEN_VHT_3895;
+		break;
+	}
+
+	ieee80211_sta_recalc_aggregates(&link_sta->sta->sta);
+}