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 --- arch/alpha/boot/stdio.c | 302 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 302 insertions(+) create mode 100644 arch/alpha/boot/stdio.c (limited to 'arch/alpha/boot/stdio.c') diff --git a/arch/alpha/boot/stdio.c b/arch/alpha/boot/stdio.c new file mode 100644 index 000000000..faa5234b9 --- /dev/null +++ b/arch/alpha/boot/stdio.c @@ -0,0 +1,302 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) Paul Mackerras 1997. + */ +#include +#include + +size_t strnlen(const char * s, size_t count) +{ + const char *sc; + + for (sc = s; count-- && *sc != '\0'; ++sc) + /* nothing */; + return sc - s; +} + +# define do_div(n, base) ({ \ + unsigned int __base = (base); \ + unsigned int __rem; \ + __rem = ((unsigned long long)(n)) % __base; \ + (n) = ((unsigned long long)(n)) / __base; \ + __rem; \ +}) + + +static int skip_atoi(const char **s) +{ + int i, c; + + for (i = 0; '0' <= (c = **s) && c <= '9'; ++*s) + i = i*10 + c - '0'; + return i; +} + +#define ZEROPAD 1 /* pad with zero */ +#define SIGN 2 /* unsigned/signed long */ +#define PLUS 4 /* show plus */ +#define SPACE 8 /* space if plus */ +#define LEFT 16 /* left justified */ +#define SPECIAL 32 /* 0x */ +#define LARGE 64 /* use 'ABCDEF' instead of 'abcdef' */ + +static char * number(char * str, unsigned long long num, int base, int size, int precision, int type) +{ + char c, sign, tmp[66]; + const char *digits = "0123456789abcdefghijklmnopqrstuvwxyz"; + int i; + + if (type & LARGE) + digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; + if (type & LEFT) + type &= ~ZEROPAD; + if (base < 2 || base > 36) + return 0; + c = (type & ZEROPAD) ? '0' : ' '; + sign = 0; + if (type & SIGN) { + if ((signed long long)num < 0) { + sign = '-'; + num = - (signed long long)num; + size--; + } else if (type & PLUS) { + sign = '+'; + size--; + } else if (type & SPACE) { + sign = ' '; + size--; + } + } + if (type & SPECIAL) { + if (base == 16) + size -= 2; + else if (base == 8) + size--; + } + i = 0; + if (num == 0) + tmp[i++]='0'; + else while (num != 0) { + tmp[i++] = digits[do_div(num, base)]; + } + if (i > precision) + precision = i; + size -= precision; + if (!(type&(ZEROPAD+LEFT))) + while (size-- > 0) + *str++ = ' '; + if (sign) + *str++ = sign; + if (type & SPECIAL) { + if (base==8) + *str++ = '0'; + else if (base == 16) { + *str++ = '0'; + *str++ = digits[33]; + } + } + if (!(type & LEFT)) + while (size-- > 0) + *str++ = c; + while (i < precision--) + *str++ = '0'; + while (i-- > 0) + *str++ = tmp[i]; + while (size-- > 0) + *str++ = ' '; + return str; +} + +int vsprintf(char *buf, const char *fmt, va_list args) +{ + int len; + unsigned long long num; + int i, base; + char * str; + const char *s; + + int flags; /* flags to number() */ + + int field_width; /* width of output field */ + int precision; /* min. # of digits for integers; max + number of chars for from string */ + int qualifier; /* 'h', 'l', or 'L' for integer fields */ + /* 'z' support added 23/7/1999 S.H. */ + /* 'z' changed to 'Z' --davidm 1/25/99 */ + + + for (str = buf ; *fmt ; ++fmt) { + if (*fmt != '%') { + *str++ = *fmt; + continue; + } + + /* process flags */ + flags = 0; + repeat: + ++fmt; /* this also skips first '%' */ + switch (*fmt) { + case '-': flags |= LEFT; goto repeat; + case '+': flags |= PLUS; goto repeat; + case ' ': flags |= SPACE; goto repeat; + case '#': flags |= SPECIAL; goto repeat; + case '0': flags |= ZEROPAD; goto repeat; + } + + /* get field width */ + field_width = -1; + if ('0' <= *fmt && *fmt <= '9') + field_width = skip_atoi(&fmt); + else if (*fmt == '*') { + ++fmt; + /* it's the next argument */ + field_width = va_arg(args, int); + if (field_width < 0) { + field_width = -field_width; + flags |= LEFT; + } + } + + /* get the precision */ + precision = -1; + if (*fmt == '.') { + ++fmt; + if ('0' <= *fmt && *fmt <= '9') + precision = skip_atoi(&fmt); + else if (*fmt == '*') { + ++fmt; + /* it's the next argument */ + precision = va_arg(args, int); + } + if (precision < 0) + precision = 0; + } + + /* get the conversion qualifier */ + qualifier = -1; + if (*fmt == 'l' && *(fmt + 1) == 'l') { + qualifier = 'q'; + fmt += 2; + } else if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L' + || *fmt == 'Z') { + qualifier = *fmt; + ++fmt; + } + + /* default base */ + base = 10; + + switch (*fmt) { + case 'c': + if (!(flags & LEFT)) + while (--field_width > 0) + *str++ = ' '; + *str++ = (unsigned char) va_arg(args, int); + while (--field_width > 0) + *str++ = ' '; + continue; + + case 's': + s = va_arg(args, char *); + if (!s) + s = ""; + + len = strnlen(s, precision); + + if (!(flags & LEFT)) + while (len < field_width--) + *str++ = ' '; + for (i = 0; i < len; ++i) + *str++ = *s++; + while (len < field_width--) + *str++ = ' '; + continue; + + case 'p': + if (field_width == -1) { + field_width = 2*sizeof(void *); + flags |= ZEROPAD; + } + str = number(str, + (unsigned long) va_arg(args, void *), 16, + field_width, precision, flags); + continue; + + + case 'n': + if (qualifier == 'l') { + long * ip = va_arg(args, long *); + *ip = (str - buf); + } else if (qualifier == 'Z') { + size_t * ip = va_arg(args, size_t *); + *ip = (str - buf); + } else { + int * ip = va_arg(args, int *); + *ip = (str - buf); + } + continue; + + case '%': + *str++ = '%'; + continue; + + /* integer number formats - set up the flags and "break" */ + case 'o': + base = 8; + break; + + case 'X': + flags |= LARGE; + case 'x': + base = 16; + break; + + case 'd': + case 'i': + flags |= SIGN; + case 'u': + break; + + default: + *str++ = '%'; + if (*fmt) + *str++ = *fmt; + else + --fmt; + continue; + } + if (qualifier == 'l') { + num = va_arg(args, unsigned long); + if (flags & SIGN) + num = (signed long) num; + } else if (qualifier == 'q') { + num = va_arg(args, unsigned long long); + if (flags & SIGN) + num = (signed long long) num; + } else if (qualifier == 'Z') { + num = va_arg(args, size_t); + } else if (qualifier == 'h') { + num = (unsigned short) va_arg(args, int); + if (flags & SIGN) + num = (signed short) num; + } else { + num = va_arg(args, unsigned int); + if (flags & SIGN) + num = (signed int) num; + } + str = number(str, num, base, field_width, precision, flags); + } + *str = '\0'; + return str-buf; +} + +int sprintf(char * buf, const char *fmt, ...) +{ + va_list args; + int i; + + va_start(args, fmt); + i = vsprintf(buf, fmt, args); + va_end(args); + return i; +} -- cgit v1.3.1