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, 476 insertions, 0 deletions

diff --git a/fs/btrfs/tests/chunk-allocation-tests.c b/fs/btrfs/tests/chunk-allocation-tests.c
new file mode 100644
index 000000000..9beb0602f
--- /dev/null
+++ b/fs/btrfs/tests/chunk-allocation-tests.c
@@ -0,0 +1,476 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2026 Meta.  All rights reserved.
+ */
+
+#include <linux/sizes.h>
+#include "btrfs-tests.h"
+#include "../volumes.h"
+#include "../disk-io.h"
+#include "../extent-io-tree.h"
+
+/*
+ * Tests for chunk allocator pending extent internals.
+ * These two functions form the core of searching the chunk allocation pending
+ * extent bitmap and have relatively easily definable semantics, so unit
+ * testing them can help ensure the correctness of chunk allocation.
+ */
+
+/*
+ * Describes the inputs to the system and expected results
+ * when testing btrfs_find_hole_in_pending_extents().
+ */
+struct pending_extent_test_case {
+	const char *name;
+	/* Input range to search. */
+	u64 hole_start;
+	u64 hole_len;
+	/* The size of hole we are searching for. */
+	u64 min_hole_size;
+	/*
+	 * Pending extents to set up (up to 2 for up to 3 holes)
+	 * If len == 0, then it is skipped.
+	 */
+	struct {
+		u64 start;
+		u64 len;
+	} pending_extents[2];
+	/* Expected outputs. */
+	bool expected_found;
+	u64 expected_start;
+	u64 expected_len;
+};
+
+static const struct pending_extent_test_case find_hole_tests[] = {
+	{
+		.name = "no pending extents",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_1G,
+		.pending_extents = { },
+		.expected_found = true,
+		.expected_start = 0,
+		.expected_len = 10ULL * SZ_1G,
+	},
+	{
+		.name = "pending extent at start of range",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_1G,
+		.pending_extents = {
+			{ .start = 0, .len = SZ_1G },
+		},
+		.expected_found = true,
+		.expected_start = SZ_1G,
+		.expected_len = 9ULL * SZ_1G,
+	},
+	{
+		.name = "pending extent overlapping start of range",
+		.hole_start = SZ_1G,
+		.hole_len = 9ULL * SZ_1G,
+		.min_hole_size = SZ_1G,
+		.pending_extents = {
+			{ .start = 0, .len = SZ_2G },
+		},
+		.expected_found = true,
+		.expected_start = SZ_2G,
+		.expected_len = 8ULL * SZ_1G,
+	},
+	{
+		.name = "two holes; first hole is exactly big enough",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_1G,
+		.pending_extents = {
+			{ .start = SZ_1G, .len = SZ_1G },
+		},
+		.expected_found = true,
+		.expected_start = 0,
+		.expected_len = SZ_1G,
+	},
+	{
+		.name = "two holes; first hole is big enough",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_1G,
+		.pending_extents = {
+			{ .start = SZ_2G, .len = SZ_1G },
+		},
+		.expected_found = true,
+		.expected_start = 0,
+		.expected_len = SZ_2G,
+	},
+	{
+		.name = "two holes; second hole is big enough",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_2G,
+		.pending_extents = {
+			{ .start = SZ_1G, .len = SZ_1G },
+		},
+		.expected_found = true,
+		.expected_start = SZ_2G,
+		.expected_len = 8ULL * SZ_1G,
+	},
+	{
+		.name = "three holes; first hole big enough",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_2G,
+		.pending_extents = {
+			{ .start = SZ_2G, .len = SZ_1G },
+			{ .start = 4ULL * SZ_1G, .len = SZ_1G },
+		},
+		.expected_found = true,
+		.expected_start = 0,
+		.expected_len = SZ_2G,
+	},
+	{
+		.name = "three holes; second hole big enough",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_2G,
+		.pending_extents = {
+			{ .start = SZ_1G, .len = SZ_1G },
+			{ .start = 5ULL * SZ_1G, .len = SZ_1G },
+		},
+		.expected_found = true,
+		.expected_start = SZ_2G,
+		.expected_len = 3ULL * SZ_1G,
+	},
+	{
+		.name = "three holes; third hole big enough",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_2G,
+		.pending_extents = {
+			{ .start = SZ_1G, .len = SZ_1G },
+			{ .start = 3ULL * SZ_1G, .len = 5ULL * SZ_1G },
+		},
+		.expected_found = true,
+		.expected_start = 8ULL * SZ_1G,
+		.expected_len = SZ_2G,
+	},
+	{
+		.name = "three holes; all holes too small",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_2G,
+		.pending_extents = {
+			{ .start = SZ_1G, .len = SZ_1G },
+			{ .start = 3ULL * SZ_1G, .len = 6ULL * SZ_1G },
+		},
+		.expected_found = false,
+		.expected_start = 0,
+		.expected_len = SZ_1G,
+	},
+	{
+		.name = "three holes; all holes too small; first biggest",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = 3ULL * SZ_1G,
+		.pending_extents = {
+			{ .start = SZ_2G, .len = SZ_1G },
+			{ .start = 4ULL * SZ_1G, .len = 5ULL * SZ_1G },
+		},
+		.expected_found = false,
+		.expected_start = 0,
+		.expected_len = SZ_2G,
+	},
+	{
+		.name = "three holes; all holes too small; second biggest",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = 3ULL * SZ_1G,
+		.pending_extents = {
+			{ .start = SZ_1G, .len = SZ_1G },
+			{ .start = 4ULL * SZ_1G, .len = 5ULL * SZ_1G },
+		},
+		.expected_found = false,
+		.expected_start = SZ_2G,
+		.expected_len = SZ_2G,
+	},
+	{
+		.name = "three holes; all holes too small; third biggest",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = 3ULL * SZ_1G,
+		.pending_extents = {
+			{ .start = SZ_1G, .len = SZ_1G },
+			{ .start = 3ULL * SZ_1G, .len = 5ULL * SZ_1G },
+		},
+		.expected_found = false,
+		.expected_start = 8ULL * SZ_1G,
+		.expected_len = SZ_2G,
+	},
+	{
+		.name = "hole entirely allocated by pending",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_1G,
+		.pending_extents = {
+			{ .start = 0, .len = 10ULL * SZ_1G },
+		},
+		.expected_found = false,
+		.expected_start = 10ULL * SZ_1G,
+		.expected_len = 0,
+	},
+	{
+		.name = "pending extent at end of range",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.min_hole_size = SZ_1G,
+		.pending_extents = {
+			{ .start = 9ULL * SZ_1G, .len = SZ_2G },
+		},
+		.expected_found = true,
+		.expected_start = 0,
+		.expected_len = 9ULL * SZ_1G,
+	},
+	{
+		.name = "zero length input",
+		.hole_start = SZ_1G,
+		.hole_len = 0,
+		.min_hole_size = SZ_1G,
+		.pending_extents = { },
+		.expected_found = false,
+		.expected_start = SZ_1G,
+		.expected_len = 0,
+	},
+};
+
+static int test_find_hole_in_pending(u32 sectorsize, u32 nodesize)
+{
+	struct btrfs_fs_info *fs_info;
+	struct btrfs_device *device;
+	int ret = 0;
+
+	test_msg("running find_hole_in_pending_extents tests");
+
+	fs_info = btrfs_alloc_dummy_fs_info(nodesize, sectorsize);
+	if (!fs_info) {
+		test_std_err(TEST_ALLOC_FS_INFO);
+		return -ENOMEM;
+	}
+
+	device = btrfs_alloc_dummy_device(fs_info);
+	if (IS_ERR(device)) {
+		test_err("failed to allocate dummy device");
+		ret = PTR_ERR(device);
+		goto out_free_fs_info;
+	}
+	device->fs_info = fs_info;
+
+	for (int i = 0; i < ARRAY_SIZE(find_hole_tests); i++) {
+		const struct pending_extent_test_case *test_case = &find_hole_tests[i];
+		u64 hole_start = test_case->hole_start;
+		u64 hole_len = test_case->hole_len;
+		bool found;
+
+		for (int j = 0; j < ARRAY_SIZE(test_case->pending_extents); j++) {
+			u64 start = test_case->pending_extents[j].start;
+			u64 len = test_case->pending_extents[j].len;
+
+			if (!len)
+				continue;
+			btrfs_set_extent_bit(&device->alloc_state,
+					     start, start + len - 1,
+					     CHUNK_ALLOCATED, NULL);
+		}
+
+		mutex_lock(&fs_info->chunk_mutex);
+		found = btrfs_find_hole_in_pending_extents(device, &hole_start, &hole_len,
+							   test_case->min_hole_size);
+		mutex_unlock(&fs_info->chunk_mutex);
+
+		if (found != test_case->expected_found) {
+			test_err("%s: expected found=%d, got found=%d",
+				 test_case->name, test_case->expected_found, found);
+			ret = -EINVAL;
+			goto out_clear_pending_extents;
+		}
+		if (hole_start != test_case->expected_start ||
+		    hole_len != test_case->expected_len) {
+			test_err("%s: expected [%llu, %llu), got [%llu, %llu)",
+				 test_case->name, test_case->expected_start,
+				 test_case->expected_start +
+					 test_case->expected_len,
+				 hole_start, hole_start + hole_len);
+			ret = -EINVAL;
+			goto out_clear_pending_extents;
+		}
+out_clear_pending_extents:
+		btrfs_clear_extent_bit(&device->alloc_state, 0, (u64)-1,
+				       CHUNK_ALLOCATED, NULL);
+		if (ret)
+			break;
+	}
+
+out_free_fs_info:
+	btrfs_free_dummy_fs_info(fs_info);
+	return ret;
+}
+
+/*
+ * Describes the inputs to the system and expected results
+ * when testing btrfs_first_pending_extent().
+ */
+struct first_pending_test_case {
+	const char *name;
+	/* The range to look for a pending extent in. */
+	u64 hole_start;
+	u64 hole_len;
+	/* The pending extent to look for. */
+	struct {
+		u64 start;
+		u64 len;
+	} pending_extent;
+	/* Expected outputs. */
+	bool expected_found;
+	u64 expected_pending_start;
+	u64 expected_pending_end;
+};
+
+static const struct first_pending_test_case first_pending_tests[] = {
+	{
+		.name = "no pending extent",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.pending_extent = { 0, 0 },
+		.expected_found = false,
+	},
+	{
+		.name = "pending extent at search start",
+		.hole_start = SZ_1G,
+		.hole_len = 9ULL * SZ_1G,
+		.pending_extent = { SZ_1G, SZ_1G },
+		.expected_found = true,
+		.expected_pending_start = SZ_1G,
+		.expected_pending_end = SZ_2G - 1,
+	},
+	{
+		.name = "pending extent overlapping search start",
+		.hole_start = SZ_1G,
+		.hole_len = 9ULL * SZ_1G,
+		.pending_extent = { 0, SZ_2G },
+		.expected_found = true,
+		.expected_pending_start = 0,
+		.expected_pending_end = SZ_2G - 1,
+	},
+	{
+		.name = "pending extent inside search range",
+		.hole_start = 0,
+		.hole_len = 10ULL * SZ_1G,
+		.pending_extent = { SZ_2G, SZ_1G },
+		.expected_found = true,
+		.expected_pending_start = SZ_2G,
+		.expected_pending_end = 3ULL * SZ_1G - 1,
+	},
+	{
+		.name = "pending extent outside search range",
+		.hole_start = 0,
+		.hole_len = SZ_1G,
+		.pending_extent = { SZ_2G, SZ_1G },
+		.expected_found = false,
+	},
+	{
+		.name = "pending extent overlapping end of search range",
+		.hole_start = 0,
+		.hole_len = SZ_2G,
+		.pending_extent = { SZ_1G, SZ_2G },
+		.expected_found = true,
+		.expected_pending_start = SZ_1G,
+		.expected_pending_end = 3ULL * SZ_1G - 1,
+	},
+};
+
+static int test_first_pending_extent(u32 sectorsize, u32 nodesize)
+{
+	struct btrfs_fs_info *fs_info;
+	struct btrfs_device *device;
+	int ret = 0;
+
+	test_msg("running first_pending_extent tests");
+
+	fs_info = btrfs_alloc_dummy_fs_info(nodesize, sectorsize);
+	if (!fs_info) {
+		test_std_err(TEST_ALLOC_FS_INFO);
+		return -ENOMEM;
+	}
+
+	device = btrfs_alloc_dummy_device(fs_info);
+	if (IS_ERR(device)) {
+		test_err("failed to allocate dummy device");
+		ret = PTR_ERR(device);
+		goto out_free_fs_info;
+	}
+
+	device->fs_info = fs_info;
+
+	for (int i = 0; i < ARRAY_SIZE(first_pending_tests); i++) {
+		const struct first_pending_test_case *test_case = &first_pending_tests[i];
+		u64 start = test_case->pending_extent.start;
+		u64 len = test_case->pending_extent.len;
+		u64 pending_start, pending_end;
+		bool found;
+
+		if (len) {
+			btrfs_set_extent_bit(&device->alloc_state,
+					     start, start + len - 1,
+					     CHUNK_ALLOCATED, NULL);
+		}
+
+		mutex_lock(&fs_info->chunk_mutex);
+		found = btrfs_first_pending_extent(device, test_case->hole_start,
+						   test_case->hole_len,
+						   &pending_start, &pending_end);
+		mutex_unlock(&fs_info->chunk_mutex);
+
+		if (found != test_case->expected_found) {
+			test_err("%s: expected found=%d, got found=%d",
+				 test_case->name, test_case->expected_found, found);
+			ret = -EINVAL;
+			goto out_clear_pending_extents;
+		}
+		if (!found)
+			goto out_clear_pending_extents;
+
+		if (pending_start != test_case->expected_pending_start ||
+		    pending_end != test_case->expected_pending_end) {
+			test_err("%s: expected pending [%llu, %llu], got [%llu, %llu]",
+				 test_case->name,
+				 test_case->expected_pending_start,
+				 test_case->expected_pending_end,
+				 pending_start, pending_end);
+			ret = -EINVAL;
+			goto out_clear_pending_extents;
+		}
+
+out_clear_pending_extents:
+		btrfs_clear_extent_bit(&device->alloc_state, 0, (u64)-1,
+				       CHUNK_ALLOCATED, NULL);
+		if (ret)
+			break;
+	}
+
+out_free_fs_info:
+	btrfs_free_dummy_fs_info(fs_info);
+	return ret;
+}
+
+int btrfs_test_chunk_allocation(u32 sectorsize, u32 nodesize)
+{
+	int ret;
+
+	test_msg("running chunk allocation tests");
+
+	ret = test_first_pending_extent(sectorsize, nodesize);
+	if (ret)
+		return ret;
+
+	ret = test_find_hole_in_pending(sectorsize, nodesize);
+	if (ret)
+		return ret;
+
+	return 0;
+}