From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- samples/auxdisplay/.gitignore | 2 + samples/auxdisplay/Makefile | 2 + samples/auxdisplay/cfag12864b-example.c | 267 ++++++++++++++++++++++++++++++++ 3 files changed, 271 insertions(+) create mode 100644 samples/auxdisplay/.gitignore create mode 100644 samples/auxdisplay/Makefile create mode 100644 samples/auxdisplay/cfag12864b-example.c (limited to 'samples/auxdisplay') diff --git a/samples/auxdisplay/.gitignore b/samples/auxdisplay/.gitignore new file mode 100644 index 000000000..d02381684 --- /dev/null +++ b/samples/auxdisplay/.gitignore @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0-only +/cfag12864b-example diff --git a/samples/auxdisplay/Makefile b/samples/auxdisplay/Makefile new file mode 100644 index 000000000..19d556893 --- /dev/null +++ b/samples/auxdisplay/Makefile @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0 +userprogs-always-y += cfag12864b-example diff --git a/samples/auxdisplay/cfag12864b-example.c b/samples/auxdisplay/cfag12864b-example.c new file mode 100644 index 000000000..2e3bb7375 --- /dev/null +++ b/samples/auxdisplay/cfag12864b-example.c @@ -0,0 +1,267 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Filename: cfag12864b-example.c + * Version: 0.1.0 + * Description: cfag12864b LCD userspace example program + * + * Author: Copyright (C) Miguel Ojeda + * Date: 2006-10-31 + */ + +/* + * ------------------------ + * start of cfag12864b code + * ------------------------ + */ + +#include +#include +#include +#include +#include +#include + +#define CFAG12864B_WIDTH (128) +#define CFAG12864B_HEIGHT (64) +#define CFAG12864B_SIZE (128 * 64 / 8) +#define CFAG12864B_BPB (8) +#define CFAG12864B_ADDRESS(x, y) ((y) * CFAG12864B_WIDTH / \ + CFAG12864B_BPB + (x) / CFAG12864B_BPB) +#define CFAG12864B_BIT(n) (((unsigned char) 1) << (n)) + +#undef CFAG12864B_DOCHECK +#ifdef CFAG12864B_DOCHECK + #define CFAG12864B_CHECK(x, y) ((x) < CFAG12864B_WIDTH && \ + (y) < CFAG12864B_HEIGHT) +#else + #define CFAG12864B_CHECK(x, y) (1) +#endif + +int cfag12864b_fd; +unsigned char * cfag12864b_mem; +unsigned char cfag12864b_buffer[CFAG12864B_SIZE]; + +/* + * init a cfag12864b framebuffer device + * + * No error: return = 0 + * Unable to open: return = -1 + * Unable to mmap: return = -2 + */ +static int cfag12864b_init(char *path) +{ + cfag12864b_fd = open(path, O_RDWR); + if (cfag12864b_fd == -1) + return -1; + + cfag12864b_mem = mmap(0, CFAG12864B_SIZE, PROT_READ | PROT_WRITE, + MAP_SHARED, cfag12864b_fd, 0); + if (cfag12864b_mem == MAP_FAILED) { + close(cfag12864b_fd); + return -2; + } + + return 0; +} + +/* + * exit a cfag12864b framebuffer device + */ +static void cfag12864b_exit(void) +{ + munmap(cfag12864b_mem, CFAG12864B_SIZE); + close(cfag12864b_fd); +} + +/* + * set (x, y) pixel + */ +static void cfag12864b_set(unsigned char x, unsigned char y) +{ + if (CFAG12864B_CHECK(x, y)) + cfag12864b_buffer[CFAG12864B_ADDRESS(x, y)] |= + CFAG12864B_BIT(x % CFAG12864B_BPB); +} + +/* + * unset (x, y) pixel + */ +static void cfag12864b_unset(unsigned char x, unsigned char y) +{ + if (CFAG12864B_CHECK(x, y)) + cfag12864b_buffer[CFAG12864B_ADDRESS(x, y)] &= + ~CFAG12864B_BIT(x % CFAG12864B_BPB); +} + +/* + * is set (x, y) pixel? + * + * Pixel off: return = 0 + * Pixel on: return = 1 + */ +static unsigned char cfag12864b_isset(unsigned char x, unsigned char y) +{ + if (CFAG12864B_CHECK(x, y)) + if (cfag12864b_buffer[CFAG12864B_ADDRESS(x, y)] & + CFAG12864B_BIT(x % CFAG12864B_BPB)) + return 1; + + return 0; +} + +/* + * not (x, y) pixel + */ +static void cfag12864b_not(unsigned char x, unsigned char y) +{ + if (cfag12864b_isset(x, y)) + cfag12864b_unset(x, y); + else + cfag12864b_set(x, y); +} + +/* + * fill (set all pixels) + */ +static void cfag12864b_fill(void) +{ + unsigned short i; + + for (i = 0; i < CFAG12864B_SIZE; i++) + cfag12864b_buffer[i] = 0xFF; +} + +/* + * clear (unset all pixels) + */ +static void cfag12864b_clear(void) +{ + unsigned short i; + + for (i = 0; i < CFAG12864B_SIZE; i++) + cfag12864b_buffer[i] = 0; +} + +/* + * format a [128*64] matrix + * + * Pixel off: src[i] = 0 + * Pixel on: src[i] > 0 + */ +static void cfag12864b_format(unsigned char * matrix) +{ + unsigned char i, j, n; + + for (i = 0; i < CFAG12864B_HEIGHT; i++) + for (j = 0; j < CFAG12864B_WIDTH / CFAG12864B_BPB; j++) { + cfag12864b_buffer[i * CFAG12864B_WIDTH / CFAG12864B_BPB + + j] = 0; + for (n = 0; n < CFAG12864B_BPB; n++) + if (matrix[i * CFAG12864B_WIDTH + + j * CFAG12864B_BPB + n]) + cfag12864b_buffer[i * CFAG12864B_WIDTH / + CFAG12864B_BPB + j] |= + CFAG12864B_BIT(n); + } +} + +/* + * blit buffer to lcd + */ +static void cfag12864b_blit(void) +{ + memcpy(cfag12864b_mem, cfag12864b_buffer, CFAG12864B_SIZE); +} + +/* + * ---------------------- + * end of cfag12864b code + * ---------------------- + */ + +#include + +#define EXAMPLES 6 + +static void example(unsigned char n) +{ + unsigned short i, j; + unsigned char matrix[CFAG12864B_WIDTH * CFAG12864B_HEIGHT]; + + if (n > EXAMPLES) + return; + + printf("Example %i/%i - ", n, EXAMPLES); + + switch (n) { + case 1: + printf("Draw points setting bits"); + cfag12864b_clear(); + for (i = 0; i < CFAG12864B_WIDTH; i += 2) + for (j = 0; j < CFAG12864B_HEIGHT; j += 2) + cfag12864b_set(i, j); + break; + + case 2: + printf("Clear the LCD"); + cfag12864b_clear(); + break; + + case 3: + printf("Draw rows formatting a [128*64] matrix"); + memset(matrix, 0, CFAG12864B_WIDTH * CFAG12864B_HEIGHT); + for (i = 0; i < CFAG12864B_WIDTH; i++) + for (j = 0; j < CFAG12864B_HEIGHT; j += 2) + matrix[j * CFAG12864B_WIDTH + i] = 1; + cfag12864b_format(matrix); + break; + + case 4: + printf("Fill the lcd"); + cfag12864b_fill(); + break; + + case 5: + printf("Draw columns unsetting bits"); + for (i = 0; i < CFAG12864B_WIDTH; i += 2) + for (j = 0; j < CFAG12864B_HEIGHT; j++) + cfag12864b_unset(i, j); + break; + + case 6: + printf("Do negative not-ing all bits"); + for (i = 0; i < CFAG12864B_WIDTH; i++) + for (j = 0; j < CFAG12864B_HEIGHT; j ++) + cfag12864b_not(i, j); + break; + } + + puts(" - [Press Enter]"); +} + +int main(int argc, char *argv[]) +{ + unsigned char n; + + if (argc != 2) { + printf( + "Syntax: %s fbdev\n" + "Usually: /dev/fb0, /dev/fb1...\n", argv[0]); + return -1; + } + + if (cfag12864b_init(argv[1])) { + printf("Can't init %s fbdev\n", argv[1]); + return -2; + } + + for (n = 1; n <= EXAMPLES; n++) { + example(n); + cfag12864b_blit(); + while (getchar() != '\n'); + } + + cfag12864b_exit(); + + return 0; +} -- cgit v1.3.1