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, 151 insertions, 0 deletions

diff --git a/fs/lockd/svcshare.c b/fs/lockd/svcshare.c
new file mode 100644
index 000000000..a58b7035b
--- /dev/null
+++ b/fs/lockd/svcshare.c
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/lockd/svcshare.c
+ *
+ * Management of DOS shares.
+ *
+ * Copyright (C) 1996 Olaf Kirch <okir@monad.swb.de>
+ */
+
+#include <linux/time.h>
+#include <linux/unistd.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+
+#include <linux/sunrpc/clnt.h>
+#include <linux/sunrpc/svc.h>
+
+#include "lockd.h"
+#include "share.h"
+
+static inline int
+nlm_cmp_owner(struct lockd_share *share, struct xdr_netobj *oh)
+{
+	return share->s_owner.len == oh->len
+	    && !memcmp(share->s_owner.data, oh->data, oh->len);
+}
+
+/*
+ * Recompute s_access / s_mode as the union of every (access, deny) pair
+ * whose bit is currently set in s_access_deny_bmap.
+ */
+static void nlm_recompute_share(struct lockd_share *share)
+{
+	u32 new_access = 0, new_mode = 0;
+	unsigned int i;
+
+	for (i = 0; i < 16; i++) {
+		if (share->s_access_deny_bmap & BIT(i)) {
+			new_access |= i >> 2;
+			new_mode   |= i & 3;
+		}
+	}
+	share->s_access = new_access;
+	share->s_mode = new_mode;
+}
+
+/**
+ * nlmsvc_share_file - create a share
+ * @host: Network client peer
+ * @file: File to be shared
+ * @oh: Share owner handle
+ * @access: Requested access mode
+ * @mode: Requested file sharing mode
+ *
+ * Returns an NLM status code.
+ */
+__be32
+nlmsvc_share_file(struct nlm_host *host, struct nlm_file *file,
+		  struct xdr_netobj *oh, u32 access, u32 mode)
+{
+	struct lockd_share	*share;
+	u8			*ohdata;
+
+	if (nlmsvc_file_cannot_lock(file))
+		return nlm_lck_denied_nolocks;
+
+	for (share = file->f_shares; share; share = share->s_next) {
+		if (share->s_host == host && nlm_cmp_owner(share, oh))
+			goto update;
+		if ((access & share->s_mode) || (mode & share->s_access))
+			return nlm_lck_denied;
+	}
+
+	share = kmalloc(sizeof(*share) + oh->len, GFP_KERNEL);
+	if (share == NULL)
+		return nlm_lck_denied_nolocks;
+
+	/* Copy owner handle */
+	ohdata = (u8 *) (share + 1);
+	memcpy(ohdata, oh->data, oh->len);
+
+	share->s_file	    = file;
+	share->s_host       = host;
+	share->s_owner.data = ohdata;
+	share->s_owner.len  = oh->len;
+	share->s_access_deny_bmap  = 0;
+	share->s_next       = file->f_shares;
+	file->f_shares      = share;
+
+update:
+	share->s_access_deny_bmap |= LOCKD_FSH_BIT(access, mode);
+	nlm_recompute_share(share);
+	return nlm_granted;
+}
+
+/**
+ * nlmsvc_unshare_file - delete a share
+ * @host: Network client peer
+ * @file: File to be unshared
+ * @oh: Share owner handle
+ * @access: Access mode of the SHARE being released
+ * @mode: Deny mode of the SHARE being released
+ *
+ * Returns an NLM status code.
+ */
+__be32
+nlmsvc_unshare_file(struct nlm_host *host, struct nlm_file *file,
+		    struct xdr_netobj *oh, u32 access, u32 mode)
+{
+	struct lockd_share	*share, **shpp;
+
+	if (nlmsvc_file_cannot_lock(file))
+		return nlm_lck_denied_nolocks;
+
+	for (shpp = &file->f_shares; (share = *shpp) != NULL;
+					shpp = &share->s_next) {
+		if (share->s_host == host && nlm_cmp_owner(share, oh)) {
+			share->s_access_deny_bmap &= ~LOCKD_FSH_BIT(access, mode);
+			nlm_recompute_share(share);
+			if (!share->s_access_deny_bmap) {
+				*shpp = share->s_next;
+				kfree(share);
+			}
+			return nlm_granted;
+		}
+	}
+
+	/* X/Open spec says return success even if there was no
+	 * corresponding share. */
+	return nlm_granted;
+}
+
+/*
+ * Traverse all shares for a given file, and delete
+ * those owned by the given (type of) host
+ */
+void nlmsvc_traverse_shares(struct nlm_host *host, struct nlm_file *file,
+		nlm_host_match_fn_t match)
+{
+	struct lockd_share	*share, **shpp;
+
+	shpp = &file->f_shares;
+	while ((share = *shpp) !=  NULL) {
+		if (match(share->s_host, host)) {
+			*shpp = share->s_next;
+			kfree(share);
+			continue;
+		}
+		shpp = &share->s_next;
+	}
+}