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 --- fs/coda/coda_linux.c | 208 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 208 insertions(+) create mode 100644 fs/coda/coda_linux.c (limited to 'fs/coda/coda_linux.c') diff --git a/fs/coda/coda_linux.c b/fs/coda/coda_linux.c new file mode 100644 index 000000000..1d2dac95f --- /dev/null +++ b/fs/coda/coda_linux.c @@ -0,0 +1,208 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Inode operations for Coda filesystem + * Original version: (C) 1996 P. Braam and M. Callahan + * Rewritten for Linux 2.1. (C) 1997 Carnegie Mellon University + * + * Carnegie Mellon encourages users to contribute improvements to + * the Coda project. Contact Peter Braam (coda@cs.cmu.edu). + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +#include +#include "coda_psdev.h" +#include "coda_linux.h" + +/* initialize the debugging variables */ +int coda_fake_statfs; + +/* print a fid */ +char * coda_f2s(struct CodaFid *f) +{ + static char s[60]; + + sprintf(s, "(%08x.%08x.%08x.%08x)", f->opaque[0], f->opaque[1], f->opaque[2], f->opaque[3]); + + return s; +} + +/* recognize special .CONTROL name */ +int coda_iscontrol(const char *name, size_t length) +{ + return ((CODA_CONTROLLEN == length) && + (strncmp(name, CODA_CONTROL, CODA_CONTROLLEN) == 0)); +} + +unsigned short coda_flags_to_cflags(unsigned short flags) +{ + unsigned short coda_flags = 0; + + if ((flags & O_ACCMODE) == O_RDONLY) + coda_flags |= C_O_READ; + + if ((flags & O_ACCMODE) == O_RDWR) + coda_flags |= C_O_READ | C_O_WRITE; + + if ((flags & O_ACCMODE) == O_WRONLY) + coda_flags |= C_O_WRITE; + + if (flags & O_TRUNC) + coda_flags |= C_O_TRUNC; + + if (flags & O_CREAT) + coda_flags |= C_O_CREAT; + + if (flags & O_EXCL) + coda_flags |= C_O_EXCL; + + return coda_flags; +} + +static struct timespec64 coda_to_timespec64(struct coda_timespec ts) +{ + struct timespec64 ts64 = { + .tv_sec = ts.tv_sec, + .tv_nsec = ts.tv_nsec, + }; + + return ts64; +} + +static struct coda_timespec timespec64_to_coda(struct timespec64 ts64) +{ + struct coda_timespec ts = { + .tv_sec = ts64.tv_sec, + .tv_nsec = ts64.tv_nsec, + }; + + return ts; +} + +/* utility functions below */ +umode_t coda_inode_type(struct coda_vattr *attr) +{ + switch (attr->va_type) { + case C_VREG: + return S_IFREG; + case C_VDIR: + return S_IFDIR; + case C_VLNK: + return S_IFLNK; + case C_VNON: + default: + return 0; + } +} + +void coda_vattr_to_iattr(struct inode *inode, struct coda_vattr *attr) +{ + /* inode's i_flags, i_ino are set by iget + * XXX: is this all we need ?? + */ + umode_t inode_type = coda_inode_type(attr); + inode->i_mode |= inode_type; + + if (attr->va_mode != (u_short) -1) + inode->i_mode = attr->va_mode | inode_type; + if (attr->va_uid != -1) + inode->i_uid = make_kuid(&init_user_ns, (uid_t) attr->va_uid); + if (attr->va_gid != -1) + inode->i_gid = make_kgid(&init_user_ns, (gid_t) attr->va_gid); + if (attr->va_nlink != -1) + set_nlink(inode, attr->va_nlink); + if (attr->va_size != -1) + inode->i_size = attr->va_size; + if (attr->va_size != -1) + inode->i_blocks = (attr->va_size + 511) >> 9; + if (attr->va_atime.tv_sec != -1) + inode_set_atime_to_ts(inode, + coda_to_timespec64(attr->va_atime)); + if (attr->va_mtime.tv_sec != -1) + inode_set_mtime_to_ts(inode, + coda_to_timespec64(attr->va_mtime)); + if (attr->va_ctime.tv_sec != -1) + inode_set_ctime_to_ts(inode, + coda_to_timespec64(attr->va_ctime)); +} + + +/* + * BSD sets attributes that need not be modified to -1. + * Linux uses the valid field to indicate what should be + * looked at. The BSD type field needs to be deduced from linux + * mode. + * So we have to do some translations here. + */ + +void coda_iattr_to_vattr(struct iattr *iattr, struct coda_vattr *vattr) +{ + unsigned int valid; + + /* clean out */ + vattr->va_mode = -1; + vattr->va_uid = (vuid_t) -1; + vattr->va_gid = (vgid_t) -1; + vattr->va_size = (off_t) -1; + vattr->va_atime.tv_sec = (int64_t) -1; + vattr->va_atime.tv_nsec = (long) -1; + vattr->va_mtime.tv_sec = (int64_t) -1; + vattr->va_mtime.tv_nsec = (long) -1; + vattr->va_ctime.tv_sec = (int64_t) -1; + vattr->va_ctime.tv_nsec = (long) -1; + vattr->va_type = C_VNON; + vattr->va_fileid = -1; + vattr->va_gen = -1; + vattr->va_bytes = -1; + vattr->va_nlink = -1; + vattr->va_blocksize = -1; + vattr->va_rdev = -1; + vattr->va_flags = 0; + + /* determine the type */ +#if 0 + mode = iattr->ia_mode; + if ( S_ISDIR(mode) ) { + vattr->va_type = C_VDIR; + } else if ( S_ISREG(mode) ) { + vattr->va_type = C_VREG; + } else if ( S_ISLNK(mode) ) { + vattr->va_type = C_VLNK; + } else { + /* don't do others */ + vattr->va_type = C_VNON; + } +#endif + + /* set those vattrs that need change */ + valid = iattr->ia_valid; + if ( valid & ATTR_MODE ) { + vattr->va_mode = iattr->ia_mode; + } + if ( valid & ATTR_UID ) { + vattr->va_uid = (vuid_t) from_kuid(&init_user_ns, iattr->ia_uid); + } + if ( valid & ATTR_GID ) { + vattr->va_gid = (vgid_t) from_kgid(&init_user_ns, iattr->ia_gid); + } + if ( valid & ATTR_SIZE ) { + vattr->va_size = iattr->ia_size; + } + if ( valid & ATTR_ATIME ) { + vattr->va_atime = timespec64_to_coda(iattr->ia_atime); + } + if ( valid & ATTR_MTIME ) { + vattr->va_mtime = timespec64_to_coda(iattr->ia_mtime); + } + if ( valid & ATTR_CTIME ) { + vattr->va_ctime = timespec64_to_coda(iattr->ia_ctime); + } +} + -- cgit v1.3.1