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, 410 insertions, 0 deletions

diff --git a/scripts/insert-sys-cert.c b/scripts/insert-sys-cert.c
new file mode 100644
index 000000000..8902836c2
--- /dev/null
+++ b/scripts/insert-sys-cert.c
@@ -0,0 +1,410 @@
+/* Write the contents of the <certfile> into kernel symbol system_extra_cert
+ *
+ * Copyright (C) IBM Corporation, 2015
+ *
+ * Author: Mehmet Kayaalp <mkayaalp@linux.vnet.ibm.com>
+ *
+ * This software may be used and distributed according to the terms
+ * of the GNU General Public License, incorporated herein by reference.
+ *
+ * Usage: insert-sys-cert [-s <System.map> -b <vmlinux> -c <certfile>
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <ctype.h>
+#include <string.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <elf.h>
+
+#define CERT_SYM  "system_extra_cert"
+#define USED_SYM  "system_extra_cert_used"
+#define LSIZE_SYM "system_certificate_list_size"
+
+#define info(format, args...) fprintf(stderr, "INFO:    " format, ## args)
+#define warn(format, args...) fprintf(stdout, "WARNING: " format, ## args)
+#define  err(format, args...) fprintf(stderr, "ERROR:   " format, ## args)
+
+#if UINTPTR_MAX == 0xffffffff
+#define CURRENT_ELFCLASS ELFCLASS32
+#define Elf_Ehdr	Elf32_Ehdr
+#define Elf_Shdr	Elf32_Shdr
+#define Elf_Sym		Elf32_Sym
+#else
+#define CURRENT_ELFCLASS ELFCLASS64
+#define Elf_Ehdr	Elf64_Ehdr
+#define Elf_Shdr	Elf64_Shdr
+#define Elf_Sym		Elf64_Sym
+#endif
+
+static unsigned char endianness(void)
+{
+	uint16_t two_byte = 0x00FF;
+	uint8_t low_address = *((uint8_t *)&two_byte);
+
+	if (low_address == 0)
+		return ELFDATA2MSB;
+	else
+		return ELFDATA2LSB;
+}
+
+struct sym {
+	char *name;
+	unsigned long address;
+	unsigned long offset;
+	void *content;
+	int size;
+};
+
+static unsigned long get_offset_from_address(Elf_Ehdr *hdr, unsigned long addr)
+{
+	Elf_Shdr *x;
+	unsigned int i, num_sections;
+
+	x = (void *)hdr + hdr->e_shoff;
+	if (hdr->e_shnum == SHN_UNDEF)
+		num_sections = x[0].sh_size;
+	else
+		num_sections = hdr->e_shnum;
+
+	for (i = 1; i < num_sections; i++) {
+		unsigned long start = x[i].sh_addr;
+		unsigned long end = start + x[i].sh_size;
+		unsigned long offset = x[i].sh_offset;
+
+		if (addr >= start && addr <= end)
+			return addr - start + offset;
+	}
+	return 0;
+}
+
+
+#define LINE_SIZE 100
+
+static void get_symbol_from_map(Elf_Ehdr *hdr, FILE *f, char *name,
+				struct sym *s)
+{
+	char l[LINE_SIZE];
+	char *w, *p, *n;
+
+	s->size = 0;
+	s->address = 0;
+	s->offset = 0;
+	if (fseek(f, 0, SEEK_SET) != 0) {
+		perror("File seek failed");
+		exit(EXIT_FAILURE);
+	}
+	while (fgets(l, LINE_SIZE, f)) {
+		p = strchr(l, '\n');
+		if (!p) {
+			err("Missing line ending.\n");
+			return;
+		}
+		n = strstr(l, name);
+		if (n)
+			break;
+	}
+	if (!n) {
+		err("Unable to find symbol: %s\n", name);
+		return;
+	}
+	w = strchr(l, ' ');
+	if (!w)
+		return;
+
+	*w = '\0';
+	s->address = strtoul(l, NULL, 16);
+	if (s->address == 0)
+		return;
+	s->offset = get_offset_from_address(hdr, s->address);
+	s->name = name;
+	s->content = (void *)hdr + s->offset;
+}
+
+static Elf_Sym *find_elf_symbol(Elf_Ehdr *hdr, Elf_Shdr *symtab, char *name)
+{
+	Elf_Sym *sym, *symtab_start;
+	char *strtab, *symname;
+	unsigned int link;
+	Elf_Shdr *x;
+	int i, n;
+
+	x = (void *)hdr + hdr->e_shoff;
+	link = symtab->sh_link;
+	symtab_start = (void *)hdr + symtab->sh_offset;
+	n = symtab->sh_size / symtab->sh_entsize;
+	strtab = (void *)hdr + x[link].sh_offset;
+
+	for (i = 0; i < n; i++) {
+		sym = &symtab_start[i];
+		symname = strtab + sym->st_name;
+		if (strcmp(symname, name) == 0)
+			return sym;
+	}
+	err("Unable to find symbol: %s\n", name);
+	return NULL;
+}
+
+static void get_symbol_from_table(Elf_Ehdr *hdr, Elf_Shdr *symtab,
+				  char *name, struct sym *s)
+{
+	Elf_Shdr *sec;
+	int secndx;
+	Elf_Sym *elf_sym;
+	Elf_Shdr *x;
+
+	x = (void *)hdr + hdr->e_shoff;
+	s->size = 0;
+	s->address = 0;
+	s->offset = 0;
+	elf_sym = find_elf_symbol(hdr, symtab, name);
+	if (!elf_sym)
+		return;
+	secndx = elf_sym->st_shndx;
+	if (!secndx)
+		return;
+	sec = &x[secndx];
+	s->size = elf_sym->st_size;
+	s->address = elf_sym->st_value;
+	s->offset = s->address - sec->sh_addr
+			       + sec->sh_offset;
+	s->name = name;
+	s->content = (void *)hdr + s->offset;
+}
+
+static Elf_Shdr *get_symbol_table(Elf_Ehdr *hdr)
+{
+	Elf_Shdr *x;
+	unsigned int i, num_sections;
+
+	x = (void *)hdr + hdr->e_shoff;
+	if (hdr->e_shnum == SHN_UNDEF)
+		num_sections = x[0].sh_size;
+	else
+		num_sections = hdr->e_shnum;
+
+	for (i = 1; i < num_sections; i++)
+		if (x[i].sh_type == SHT_SYMTAB)
+			return &x[i];
+	return NULL;
+}
+
+static void *map_file(char *file_name, int *size)
+{
+	struct stat st;
+	void *map;
+	int fd;
+
+	fd = open(file_name, O_RDWR);
+	if (fd < 0) {
+		perror(file_name);
+		return NULL;
+	}
+	if (fstat(fd, &st)) {
+		perror("Could not determine file size");
+		close(fd);
+		return NULL;
+	}
+	*size = st.st_size;
+	map = mmap(NULL, *size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+	if (map == MAP_FAILED) {
+		perror("Mapping to memory failed");
+		close(fd);
+		return NULL;
+	}
+	close(fd);
+	return map;
+}
+
+static char *read_file(char *file_name, int *size)
+{
+	struct stat st;
+	char *buf;
+	int fd;
+
+	fd = open(file_name, O_RDONLY);
+	if (fd < 0) {
+		perror(file_name);
+		return NULL;
+	}
+	if (fstat(fd, &st)) {
+		perror("Could not determine file size");
+		close(fd);
+		return NULL;
+	}
+	*size = st.st_size;
+	buf = malloc(*size);
+	if (!buf) {
+		perror("Allocating memory failed");
+		close(fd);
+		return NULL;
+	}
+	if (read(fd, buf, *size) != *size) {
+		perror("File read failed");
+		close(fd);
+		return NULL;
+	}
+	close(fd);
+	return buf;
+}
+
+static void print_sym(Elf_Ehdr *hdr, struct sym *s)
+{
+	info("sym:    %s\n", s->name);
+	info("addr:   0x%lx\n", s->address);
+	info("size:   %d\n", s->size);
+	info("offset: 0x%lx\n", (unsigned long)s->offset);
+}
+
+static void print_usage(char *e)
+{
+	printf("Usage %s [-s <System.map>] -b <vmlinux> -c <certfile>\n", e);
+}
+
+int main(int argc, char **argv)
+{
+	char *system_map_file = NULL;
+	char *vmlinux_file = NULL;
+	char *cert_file = NULL;
+	int vmlinux_size;
+	int cert_size;
+	Elf_Ehdr *hdr;
+	char *cert;
+	FILE *system_map;
+	unsigned long *lsize;
+	int *used;
+	int opt;
+	Elf_Shdr *symtab = NULL;
+	struct sym cert_sym, lsize_sym, used_sym;
+
+	while ((opt = getopt(argc, argv, "b:c:s:")) != -1) {
+		switch (opt) {
+		case 's':
+			system_map_file = optarg;
+			break;
+		case 'b':
+			vmlinux_file = optarg;
+			break;
+		case 'c':
+			cert_file = optarg;
+			break;
+		default:
+			break;
+		}
+	}
+
+	if (!vmlinux_file || !cert_file) {
+		print_usage(argv[0]);
+		exit(EXIT_FAILURE);
+	}
+
+	cert = read_file(cert_file, &cert_size);
+	if (!cert)
+		exit(EXIT_FAILURE);
+
+	hdr = map_file(vmlinux_file, &vmlinux_size);
+	if (!hdr)
+		exit(EXIT_FAILURE);
+
+	if (vmlinux_size < sizeof(*hdr)) {
+		err("Invalid ELF file.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if ((hdr->e_ident[EI_MAG0] != ELFMAG0) ||
+	    (hdr->e_ident[EI_MAG1] != ELFMAG1) ||
+	    (hdr->e_ident[EI_MAG2] != ELFMAG2) ||
+	    (hdr->e_ident[EI_MAG3] != ELFMAG3)) {
+		err("Invalid ELF magic.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (hdr->e_ident[EI_CLASS] != CURRENT_ELFCLASS) {
+		err("ELF class mismatch.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (hdr->e_ident[EI_DATA] != endianness()) {
+		err("ELF endian mismatch.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (hdr->e_shoff > vmlinux_size) {
+		err("Could not find section header.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	symtab = get_symbol_table(hdr);
+	if (!symtab) {
+		warn("Could not find the symbol table.\n");
+		if (!system_map_file) {
+			err("Please provide a System.map file.\n");
+			print_usage(argv[0]);
+			exit(EXIT_FAILURE);
+		}
+
+		system_map = fopen(system_map_file, "r");
+		if (!system_map) {
+			perror(system_map_file);
+			exit(EXIT_FAILURE);
+		}
+		get_symbol_from_map(hdr, system_map, CERT_SYM, &cert_sym);
+		get_symbol_from_map(hdr, system_map, USED_SYM, &used_sym);
+		get_symbol_from_map(hdr, system_map, LSIZE_SYM, &lsize_sym);
+		cert_sym.size = used_sym.address - cert_sym.address;
+	} else {
+		info("Symbol table found.\n");
+		if (system_map_file)
+			warn("System.map is ignored.\n");
+		get_symbol_from_table(hdr, symtab, CERT_SYM, &cert_sym);
+		get_symbol_from_table(hdr, symtab, USED_SYM, &used_sym);
+		get_symbol_from_table(hdr, symtab, LSIZE_SYM, &lsize_sym);
+	}
+
+	if (!cert_sym.offset || !lsize_sym.offset || !used_sym.offset)
+		exit(EXIT_FAILURE);
+
+	print_sym(hdr, &cert_sym);
+	print_sym(hdr, &used_sym);
+	print_sym(hdr, &lsize_sym);
+
+	lsize = (unsigned long *)lsize_sym.content;
+	used = (int *)used_sym.content;
+
+	if (cert_sym.size < cert_size) {
+		err("Certificate is larger than the reserved area!\n");
+		exit(EXIT_FAILURE);
+	}
+
+	/* If the existing cert is the same, don't overwrite */
+	if (cert_size == *used &&
+	    strncmp(cert_sym.content, cert, cert_size) == 0) {
+		warn("Certificate was already inserted.\n");
+		exit(EXIT_SUCCESS);
+	}
+
+	if (*used > 0)
+		warn("Replacing previously inserted certificate.\n");
+
+	memcpy(cert_sym.content, cert, cert_size);
+	if (cert_size < cert_sym.size)
+		memset(cert_sym.content + cert_size,
+			0, cert_sym.size - cert_size);
+
+	*lsize = *lsize + cert_size - *used;
+	*used = cert_size;
+	info("Inserted the contents of %s into %lx.\n", cert_file,
+						cert_sym.address);
+	info("Used %d bytes out of %d bytes reserved.\n", *used,
+						 cert_sym.size);
+	exit(EXIT_SUCCESS);
+}