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, 103 insertions, 0 deletions

diff --git a/fs/netfs/stats.c b/fs/netfs/stats.c
new file mode 100644
index 000000000..ab6b916ad
--- /dev/null
+++ b/fs/netfs/stats.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Netfs support statistics
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/seq_file.h>
+#include "internal.h"
+
+atomic_t netfs_n_rh_dio_read;
+atomic_t netfs_n_rh_readahead;
+atomic_t netfs_n_rh_read_folio;
+atomic_t netfs_n_rh_read_single;
+atomic_t netfs_n_rh_rreq;
+atomic_t netfs_n_rh_sreq;
+atomic_t netfs_n_rh_download;
+atomic_t netfs_n_rh_download_done;
+atomic_t netfs_n_rh_download_failed;
+atomic_t netfs_n_rh_download_instead;
+atomic_t netfs_n_rh_read;
+atomic_t netfs_n_rh_read_done;
+atomic_t netfs_n_rh_read_failed;
+atomic_t netfs_n_rh_zero;
+atomic_t netfs_n_rh_short_read;
+atomic_t netfs_n_rh_write;
+atomic_t netfs_n_rh_write_begin;
+atomic_t netfs_n_rh_write_done;
+atomic_t netfs_n_rh_write_failed;
+atomic_t netfs_n_rh_write_zskip;
+atomic_t netfs_n_rh_retry_read_req;
+atomic_t netfs_n_rh_retry_read_subreq;
+atomic_t netfs_n_wh_buffered_write;
+atomic_t netfs_n_wh_writethrough;
+atomic_t netfs_n_wh_dio_write;
+atomic_t netfs_n_wh_writepages;
+atomic_t netfs_n_wh_copy_to_cache;
+atomic_t netfs_n_wh_wstream_conflict;
+atomic_t netfs_n_wh_upload;
+atomic_t netfs_n_wh_upload_done;
+atomic_t netfs_n_wh_upload_failed;
+atomic_t netfs_n_wh_write;
+atomic_t netfs_n_wh_write_done;
+atomic_t netfs_n_wh_write_failed;
+atomic_t netfs_n_wh_retry_write_req;
+atomic_t netfs_n_wh_retry_write_subreq;
+atomic_t netfs_n_wb_lock_skip;
+atomic_t netfs_n_wb_lock_wait;
+atomic_t netfs_n_folioq;
+
+int netfs_stats_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "Reads  : DR=%u RA=%u RF=%u RS=%u WB=%u WBZ=%u\n",
+		   atomic_read(&netfs_n_rh_dio_read),
+		   atomic_read(&netfs_n_rh_readahead),
+		   atomic_read(&netfs_n_rh_read_folio),
+		   atomic_read(&netfs_n_rh_read_single),
+		   atomic_read(&netfs_n_rh_write_begin),
+		   atomic_read(&netfs_n_rh_write_zskip));
+	seq_printf(m, "Writes : BW=%u WT=%u DW=%u WP=%u 2C=%u\n",
+		   atomic_read(&netfs_n_wh_buffered_write),
+		   atomic_read(&netfs_n_wh_writethrough),
+		   atomic_read(&netfs_n_wh_dio_write),
+		   atomic_read(&netfs_n_wh_writepages),
+		   atomic_read(&netfs_n_wh_copy_to_cache));
+	seq_printf(m, "ZeroOps: ZR=%u sh=%u sk=%u\n",
+		   atomic_read(&netfs_n_rh_zero),
+		   atomic_read(&netfs_n_rh_short_read),
+		   atomic_read(&netfs_n_rh_write_zskip));
+	seq_printf(m, "DownOps: DL=%u ds=%u df=%u di=%u\n",
+		   atomic_read(&netfs_n_rh_download),
+		   atomic_read(&netfs_n_rh_download_done),
+		   atomic_read(&netfs_n_rh_download_failed),
+		   atomic_read(&netfs_n_rh_download_instead));
+	seq_printf(m, "CaRdOps: RD=%u rs=%u rf=%u\n",
+		   atomic_read(&netfs_n_rh_read),
+		   atomic_read(&netfs_n_rh_read_done),
+		   atomic_read(&netfs_n_rh_read_failed));
+	seq_printf(m, "UpldOps: UL=%u us=%u uf=%u\n",
+		   atomic_read(&netfs_n_wh_upload),
+		   atomic_read(&netfs_n_wh_upload_done),
+		   atomic_read(&netfs_n_wh_upload_failed));
+	seq_printf(m, "CaWrOps: WR=%u ws=%u wf=%u\n",
+		   atomic_read(&netfs_n_wh_write),
+		   atomic_read(&netfs_n_wh_write_done),
+		   atomic_read(&netfs_n_wh_write_failed));
+	seq_printf(m, "Retries: rq=%u rs=%u wq=%u ws=%u\n",
+		   atomic_read(&netfs_n_rh_retry_read_req),
+		   atomic_read(&netfs_n_rh_retry_read_subreq),
+		   atomic_read(&netfs_n_wh_retry_write_req),
+		   atomic_read(&netfs_n_wh_retry_write_subreq));
+	seq_printf(m, "Objs   : rr=%u sr=%u foq=%u wsc=%u\n",
+		   atomic_read(&netfs_n_rh_rreq),
+		   atomic_read(&netfs_n_rh_sreq),
+		   atomic_read(&netfs_n_folioq),
+		   atomic_read(&netfs_n_wh_wstream_conflict));
+	seq_printf(m, "WbLock : skip=%u wait=%u\n",
+		   atomic_read(&netfs_n_wb_lock_skip),
+		   atomic_read(&netfs_n_wb_lock_wait));
+	return fscache_stats_show(m);
+}
+EXPORT_SYMBOL(netfs_stats_show);