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68025adfc1
Nathan reported [1] that when built with clang, the um kernel
crashes pretty much immediately. This turned out to be an issue
with the inline assembly I had added, when clang used %rax/%eax
for both operands. Reorder it so current->thread.segv_continue
is written first, and then the lifetime of _faulted won't have
overlap with the lifetime of segv_continue.
In the email thread Benjamin also pointed out that current->mm
is only NULL for true kernel tasks, but we could do this for a
userspace task, so the current->thread.segv_continue logic must
be lifted out of the mm==NULL check.
Finally, while looking at this, put a barrier() so the NULL
assignment to thread.segv_continue cannot be reorder before
the possibly faulting operation.
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/r/20250402221254.GA384@ax162 [1]
Fixes: d1d7f01f7c ("um: mark rodata read-only and implement _nofault accesses")
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
74 lines
2.2 KiB
C
74 lines
2.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
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* Copyright (C) 2015 Richard Weinberger (richard@nod.at)
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*/
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#ifndef __UM_UACCESS_H
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#define __UM_UACCESS_H
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#include <asm/elf.h>
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#include <linux/unaligned.h>
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#include <sysdep/faultinfo.h>
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#define __under_task_size(addr, size) \
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(((unsigned long) (addr) < TASK_SIZE) && \
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(((unsigned long) (addr) + (size)) < TASK_SIZE))
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#define __access_ok_vsyscall(addr, size) \
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(((unsigned long) (addr) >= FIXADDR_USER_START) && \
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((unsigned long) (addr) + (size) <= FIXADDR_USER_END) && \
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((unsigned long) (addr) + (size) >= (unsigned long)(addr)))
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#define __addr_range_nowrap(addr, size) \
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((unsigned long) (addr) <= ((unsigned long) (addr) + (size)))
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extern unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n);
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extern unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n);
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extern unsigned long __clear_user(void __user *mem, unsigned long len);
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static inline int __access_ok(const void __user *ptr, unsigned long size);
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/* Teach asm-generic/uaccess.h that we have C functions for these. */
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#define __access_ok __access_ok
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#define __clear_user __clear_user
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#define INLINE_COPY_FROM_USER
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#define INLINE_COPY_TO_USER
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#include <asm-generic/uaccess.h>
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static inline int __access_ok(const void __user *ptr, unsigned long size)
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{
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unsigned long addr = (unsigned long)ptr;
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return __addr_range_nowrap(addr, size) &&
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(__under_task_size(addr, size) ||
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__access_ok_vsyscall(addr, size));
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}
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#define __get_kernel_nofault(dst, src, type, err_label) \
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do { \
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int __faulted; \
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\
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___backtrack_faulted(__faulted); \
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if (__faulted) { \
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*((type *)dst) = (type) 0; \
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goto err_label; \
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} \
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*((type *)dst) = get_unaligned((type *)(src)); \
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barrier(); \
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current->thread.segv_continue = NULL; \
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} while (0)
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#define __put_kernel_nofault(dst, src, type, err_label) \
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do { \
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int __faulted; \
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\
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___backtrack_faulted(__faulted); \
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if (__faulted) \
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goto err_label; \
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put_unaligned(*((type *)src), (type *)(dst)); \
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barrier(); \
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current->thread.segv_continue = NULL; \
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} while (0)
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#endif
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