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, 248 insertions, 0 deletions

diff --git a/arch/powerpc/boot/addnote.c b/arch/powerpc/boot/addnote.c
new file mode 100644
index 000000000..787049274
--- /dev/null
+++ b/arch/powerpc/boot/addnote.c
@@ -0,0 +1,248 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Program to hack in a PT_NOTE program header entry in an ELF file.
+ * This is needed for OF on RS/6000s to load an image correctly.
+ * Note that OF needs a program header entry for the note, not an
+ * ELF section.
+ *
+ * Copyright 2000 Paul Mackerras.
+ *
+ * Adapted for 64 bit little endian images by Andrew Tauferner.
+ *
+ * Usage: addnote zImage
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+/* CHRP note section */
+static const char arch[] = "PowerPC";
+
+#define N_DESCR	6
+unsigned int descr[N_DESCR] = {
+	0xffffffff,		/* real-mode = true */
+	0x02000000,		/* real-base, i.e. where we expect OF to be */
+	0xffffffff,		/* real-size */
+	0xffffffff,		/* virt-base */
+	0xffffffff,		/* virt-size */
+	0x4000,			/* load-base */
+};
+
+/* RPA note section */
+static const char rpaname[] = "IBM,RPA-Client-Config";
+
+/*
+ * Note: setting ignore_my_client_config *should* mean that OF ignores
+ * all the other fields, but there is a firmware bug which means that
+ * it looks at the splpar field at least.  So these values need to be
+ * reasonable.
+ */
+#define N_RPA_DESCR	8
+unsigned int rpanote[N_RPA_DESCR] = {
+	0,			/* lparaffinity */
+	64,			/* min_rmo_size */
+	0,			/* min_rmo_percent */
+	40,			/* max_pft_size */
+	1,			/* splpar */
+	-1,			/* min_load */
+	0,			/* new_mem_def */
+	1,			/* ignore_my_client_config */
+};
+
+#define ROUNDUP(len)	(((len) + 3) & ~3)
+
+unsigned char buf[1024];
+#define ELFDATA2LSB     1
+#define ELFDATA2MSB     2
+static int e_data = ELFDATA2MSB;
+#define ELFCLASS32      1
+#define ELFCLASS64      2
+static int e_class = ELFCLASS32;
+
+#define GET_16BE(off)	((buf[off] << 8) + (buf[(off)+1]))
+#define GET_32BE(off)	((GET_16BE(off) << 16U) + GET_16BE((off)+2U))
+#define GET_64BE(off)	((((unsigned long long)GET_32BE(off)) << 32ULL) + \
+			((unsigned long long)GET_32BE((off)+4ULL)))
+#define PUT_16BE(off, v)(buf[off] = ((v) >> 8) & 0xff, \
+			 buf[(off) + 1] = (v) & 0xff)
+#define PUT_32BE(off, v)(PUT_16BE((off), (v) >> 16L), PUT_16BE((off) + 2, (v)))
+#define PUT_64BE(off, v)((PUT_32BE((off), (unsigned long long)(v) >> 32L), \
+			  PUT_32BE((off) + 4, (unsigned long long)(v))))
+
+#define GET_16LE(off)	((buf[off]) + (buf[(off)+1] << 8))
+#define GET_32LE(off)	(GET_16LE(off) + (GET_16LE((off)+2U) << 16U))
+#define GET_64LE(off)	((unsigned long long)GET_32LE(off) + \
+			(((unsigned long long)GET_32LE((off)+4ULL)) << 32ULL))
+#define PUT_16LE(off, v) (buf[off] = (v) & 0xff, \
+			  buf[(off) + 1] = ((v) >> 8) & 0xff)
+#define PUT_32LE(off, v) (PUT_16LE((off), (v)), PUT_16LE((off) + 2, (v) >> 16L))
+#define PUT_64LE(off, v) (PUT_32LE((off), (unsigned long long)(v)), \
+			  PUT_32LE((off) + 4, (unsigned long long)(v) >> 32L))
+
+#define GET_16(off)	(e_data == ELFDATA2MSB ? GET_16BE(off) : GET_16LE(off))
+#define GET_32(off)	(e_data == ELFDATA2MSB ? GET_32BE(off) : GET_32LE(off))
+#define GET_64(off)	(e_data == ELFDATA2MSB ? GET_64BE(off) : GET_64LE(off))
+#define PUT_16(off, v)	(e_data == ELFDATA2MSB ? PUT_16BE(off, v) : \
+			 PUT_16LE(off, v))
+#define PUT_32(off, v)  (e_data == ELFDATA2MSB ? PUT_32BE(off, v) : \
+			 PUT_32LE(off, v))
+#define PUT_64(off, v)  (e_data == ELFDATA2MSB ? PUT_64BE(off, v) : \
+			 PUT_64LE(off, v))
+
+/* Structure of an ELF file */
+#define E_IDENT		0	/* ELF header */
+#define	E_PHOFF		(e_class == ELFCLASS32 ? 28 : 32)
+#define E_PHENTSIZE	(e_class == ELFCLASS32 ? 42 : 54)
+#define E_PHNUM		(e_class == ELFCLASS32 ? 44 : 56)
+#define E_HSIZE		(e_class == ELFCLASS32 ? 52 : 64)
+
+#define EI_MAGIC	0	/* offsets in E_IDENT area */
+#define EI_CLASS	4
+#define EI_DATA		5
+
+#define PH_TYPE		0	/* ELF program header */
+#define PH_OFFSET	(e_class == ELFCLASS32 ? 4 : 8)
+#define PH_FILESZ	(e_class == ELFCLASS32 ? 16 : 32)
+#define PH_HSIZE	(e_class == ELFCLASS32 ? 32 : 56)
+
+#define PT_NOTE		4	/* Program header type = note */
+
+
+unsigned char elf_magic[4] = { 0x7f, 'E', 'L', 'F' };
+
+int
+main(int ac, char **av)
+{
+	int fd, n, i;
+	unsigned long ph, ps, np;
+	long nnote, nnote2, ns;
+
+	if (ac != 2) {
+		fprintf(stderr, "Usage: %s elf-file\n", av[0]);
+		exit(1);
+	}
+	fd = open(av[1], O_RDWR);
+	if (fd < 0) {
+		perror(av[1]);
+		exit(1);
+	}
+
+	nnote = 12 + ROUNDUP(strlen(arch) + 1) + sizeof(descr);
+	nnote2 = 12 + ROUNDUP(strlen(rpaname) + 1) + sizeof(rpanote);
+
+	n = read(fd, buf, sizeof(buf));
+	if (n < 0) {
+		perror("read");
+		exit(1);
+	}
+
+	if (memcmp(&buf[E_IDENT+EI_MAGIC], elf_magic, 4) != 0)
+		goto notelf;
+	e_class = buf[E_IDENT+EI_CLASS];
+	if (e_class != ELFCLASS32 && e_class != ELFCLASS64)
+		goto notelf;
+	e_data = buf[E_IDENT+EI_DATA];
+	if (e_data != ELFDATA2MSB && e_data != ELFDATA2LSB)
+		goto notelf;
+	if (n < E_HSIZE)
+		goto notelf;
+
+	ph = (e_class == ELFCLASS32 ? GET_32(E_PHOFF) : GET_64(E_PHOFF));
+	ps = GET_16(E_PHENTSIZE);
+	np = GET_16(E_PHNUM);
+	if (ph < E_HSIZE || ps < PH_HSIZE || np < 1)
+		goto notelf;
+	if (ph + (np + 2) * ps + nnote + nnote2 > n)
+		goto nospace;
+
+	for (i = 0; i < np; ++i) {
+		if (GET_32(ph + PH_TYPE) == PT_NOTE) {
+			fprintf(stderr, "%s already has a note entry\n",
+				av[1]);
+			exit(0);
+		}
+		ph += ps;
+	}
+
+	/* XXX check that the area we want to use is all zeroes */
+	for (i = 0; i < 2 * ps + nnote + nnote2; ++i)
+		if (buf[ph + i] != 0)
+			goto nospace;
+
+	/* fill in the program header entry */
+	ns = ph + 2 * ps;
+	PUT_32(ph + PH_TYPE, PT_NOTE);
+	if (e_class == ELFCLASS32)
+		PUT_32(ph + PH_OFFSET, ns);
+	else
+		PUT_64(ph + PH_OFFSET, ns);
+
+	if (e_class == ELFCLASS32)
+		PUT_32(ph + PH_FILESZ, nnote);
+	else
+		PUT_64(ph + PH_FILESZ, nnote);
+
+	/* fill in the note area we point to */
+	/* XXX we should probably make this a proper section */
+	PUT_32(ns, strlen(arch) + 1);
+	PUT_32(ns + 4, N_DESCR * 4);
+	PUT_32(ns + 8, 0x1275);
+	strcpy((char *) &buf[ns + 12], arch);
+	ns += 12 + strlen(arch) + 1;
+	for (i = 0; i < N_DESCR; ++i, ns += 4)
+		PUT_32BE(ns, descr[i]);
+
+	/* fill in the second program header entry and the RPA note area */
+	ph += ps;
+	PUT_32(ph + PH_TYPE, PT_NOTE);
+	if (e_class == ELFCLASS32)
+		PUT_32(ph + PH_OFFSET, ns);
+	else
+		PUT_64(ph + PH_OFFSET, ns);
+
+	if (e_class == ELFCLASS32)
+		PUT_32(ph + PH_FILESZ, nnote);
+	else
+		PUT_64(ph + PH_FILESZ, nnote2);
+
+	/* fill in the note area we point to */
+	PUT_32(ns, strlen(rpaname) + 1);
+	PUT_32(ns + 4, sizeof(rpanote));
+	PUT_32(ns + 8, 0x12759999);
+	strcpy((char *) &buf[ns + 12], rpaname);
+	ns += 12 + ROUNDUP(strlen(rpaname) + 1);
+	for (i = 0; i < N_RPA_DESCR; ++i, ns += 4)
+		PUT_32BE(ns, rpanote[i]);
+
+	/* Update the number of program headers */
+	PUT_16(E_PHNUM, np + 2);
+
+	/* write back */
+	i = lseek(fd, (long) 0, SEEK_SET);
+	if (i < 0) {
+		perror("lseek");
+		exit(1);
+	}
+	i = write(fd, buf, n);
+	if (i < 0) {
+		perror("write");
+		exit(1);
+	}
+	if (i < n) {
+		fprintf(stderr, "%s: write truncated\n", av[1]);
+		exit(1);
+	}
+
+	exit(0);
+
+ notelf:
+	fprintf(stderr, "%s does not appear to be an ELF file\n", av[1]);
+	exit(1);
+
+ nospace:
+	fprintf(stderr, "sorry, I can't find space in %s to put the note\n",
+		av[1]);
+	exit(1);
+}