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, 175 insertions, 0 deletions

diff --git a/sound/synth/util_mem.c b/sound/synth/util_mem.c
new file mode 100644
index 000000000..21893e561
--- /dev/null
+++ b/sound/synth/util_mem.c
@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (C) 2000 Takashi Iwai <tiwai@suse.de>
+ *
+ *  Generic memory management routines for soundcard memory allocation
+ */
+
+#include <linux/mutex.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <sound/core.h>
+#include <sound/util_mem.h>
+
+MODULE_AUTHOR("Takashi Iwai");
+MODULE_DESCRIPTION("Generic memory management routines for soundcard memory allocation");
+MODULE_LICENSE("GPL");
+
+#define get_memblk(p)	list_entry(p, struct snd_util_memblk, list)
+
+/*
+ * create a new memory manager
+ */
+struct snd_util_memhdr *
+snd_util_memhdr_new(int memsize)
+{
+	struct snd_util_memhdr *hdr;
+
+	hdr = kzalloc_obj(*hdr);
+	if (hdr == NULL)
+		return NULL;
+	hdr->size = memsize;
+	mutex_init(&hdr->block_mutex);
+	INIT_LIST_HEAD(&hdr->block);
+
+	return hdr;
+}
+
+/*
+ * free a memory manager
+ */
+void snd_util_memhdr_free(struct snd_util_memhdr *hdr)
+{
+	struct list_head *p;
+
+	if (!hdr)
+		return;
+	/* release all blocks */
+	while ((p = hdr->block.next) != &hdr->block) {
+		list_del(p);
+		kfree(get_memblk(p));
+	}
+	kfree(hdr);
+}
+
+/*
+ * allocate a memory block (without mutex)
+ */
+struct snd_util_memblk *
+__snd_util_mem_alloc(struct snd_util_memhdr *hdr, int size)
+{
+	struct snd_util_memblk *blk;
+	unsigned int units, prev_offset;
+	struct list_head *p;
+
+	if (snd_BUG_ON(!hdr || size <= 0))
+		return NULL;
+
+	/* word alignment */
+	units = size;
+	if (units & 1)
+		units++;
+	if (units > hdr->size)
+		return NULL;
+
+	/* look for empty block */
+	prev_offset = 0;
+	list_for_each(p, &hdr->block) {
+		blk = get_memblk(p);
+		if (blk->offset - prev_offset >= units)
+			goto __found;
+		prev_offset = blk->offset + blk->size;
+	}
+	if (hdr->size - prev_offset < units)
+		return NULL;
+
+__found:
+	return __snd_util_memblk_new(hdr, units, p->prev);
+}
+
+
+/*
+ * create a new memory block with the given size
+ * the block is linked next to prev
+ */
+struct snd_util_memblk *
+__snd_util_memblk_new(struct snd_util_memhdr *hdr, unsigned int units,
+		      struct list_head *prev)
+{
+	struct snd_util_memblk *blk;
+
+	blk = kmalloc(sizeof(struct snd_util_memblk) + hdr->block_extra_size,
+		      GFP_KERNEL);
+	if (blk == NULL)
+		return NULL;
+
+	if (prev == &hdr->block)
+		blk->offset = 0;
+	else {
+		struct snd_util_memblk *p = get_memblk(prev);
+		blk->offset = p->offset + p->size;
+	}
+	blk->size = units;
+	list_add(&blk->list, prev);
+	hdr->nblocks++;
+	hdr->used += units;
+	return blk;
+}
+
+
+/*
+ * allocate a memory block (with mutex)
+ */
+struct snd_util_memblk *
+snd_util_mem_alloc(struct snd_util_memhdr *hdr, int size)
+{
+	guard(mutex)(&hdr->block_mutex);
+	return __snd_util_mem_alloc(hdr, size);
+}
+
+
+/*
+ * remove the block from linked-list and free resource
+ * (without mutex)
+ */
+void
+__snd_util_mem_free(struct snd_util_memhdr *hdr, struct snd_util_memblk *blk)
+{
+	list_del(&blk->list);
+	hdr->nblocks--;
+	hdr->used -= blk->size;
+	kfree(blk);
+}
+
+/*
+ * free a memory block (with mutex)
+ */
+int snd_util_mem_free(struct snd_util_memhdr *hdr, struct snd_util_memblk *blk)
+{
+	if (snd_BUG_ON(!hdr || !blk))
+		return -EINVAL;
+
+	guard(mutex)(&hdr->block_mutex);
+	__snd_util_mem_free(hdr, blk);
+	return 0;
+}
+
+/*
+ * return available memory size
+ */
+int snd_util_mem_avail(struct snd_util_memhdr *hdr)
+{
+	guard(mutex)(&hdr->block_mutex);
+	return hdr->size - hdr->used;
+}
+
+
+EXPORT_SYMBOL(snd_util_memhdr_new);
+EXPORT_SYMBOL(snd_util_memhdr_free);
+EXPORT_SYMBOL(snd_util_mem_alloc);
+EXPORT_SYMBOL(snd_util_mem_free);
+EXPORT_SYMBOL(snd_util_mem_avail);
+EXPORT_SYMBOL(__snd_util_mem_alloc);
+EXPORT_SYMBOL(__snd_util_mem_free);
+EXPORT_SYMBOL(__snd_util_memblk_new);