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uaccess: reimplement probe_kernel_address() using probe_kernel_read()

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probe_kernel_address() is basically the same as the (later added)
probe_kernel_read().

The return value on EFAULT is a bit different: probe_kernel_address()
returns number-of-bytes-not-copied whereas probe_kernel_read() returns
-EFAULT.  All callers have been checked, none cared.

probe_kernel_read() can be overridden by the architecture whereas
probe_kernel_address() cannot.  parisc, blackfin and um do this, to insert
additional checking.  Hence this patch possibly fixes obscure bugs,
although there are only two probe_kernel_address() callsites outside
arch/.

My first attempt involved removing probe_kernel_address() entirely and
converting all callsites to use probe_kernel_read() directly, but that got
tiresome.

This patch shrinks mm/slab_common.o by 218 bytes.  For a single
probe_kernel_address() callsite.

Cc: Steven Miao <realmz6@gmail.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrew Morton 2015-11-05 18:46:03 -08:00 committed by Linus Torvalds
parent 86d2adccfb
commit 0ab32b6f1b
4 changed files with 17 additions and 32 deletions
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2
arch/arm/mm/alignment.c
View File

@ -803,7 +803,7 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
}
}
} else {
fault = probe_kernel_address(instrptr, instr);
fault = probe_kernel_address((void *)instrptr, instr);
instr = __mem_to_opcode_arm(instr);
}

2
arch/powerpc/sysdev/fsl_pci.c
View File

@ -999,7 +999,7 @@ int fsl_pci_mcheck_exception(struct pt_regs *regs)
ret = get_user(regs->nip, &inst);
pagefault_enable();
} else {
ret = probe_kernel_address(regs->nip, inst);
ret = probe_kernel_address((void *)regs->nip, inst);
}
if (mcheck_handle_load(regs, inst)) {

40
include/linux/uaccess.h
View File

@ -75,36 +75,6 @@ static inline unsigned long __copy_from_user_nocache(void *to,
#endif /* ARCH_HAS_NOCACHE_UACCESS */
/**
* probe_kernel_address(): safely attempt to read from a location
* @addr: address to read from - its type is type typeof(retval)*
* @retval: read into this variable
*
* Safely read from address @addr into variable @revtal. If a kernel fault
* happens, handle that and return -EFAULT.
* We ensure that the __get_user() is executed in atomic context so that
* do_page_fault() doesn't attempt to take mmap_sem. This makes
* probe_kernel_address() suitable for use within regions where the caller
* already holds mmap_sem, or other locks which nest inside mmap_sem.
* This must be a macro because __get_user() needs to know the types of the
* args.
*
* We don't include enough header files to be able to do the set_fs(). We
* require that the probe_kernel_address() caller will do that.
*/
#define probe_kernel_address(addr, retval) \
({ \
long ret; \
mm_segment_t old_fs = get_fs(); \
\
set_fs(KERNEL_DS); \
pagefault_disable(); \
ret = __copy_from_user_inatomic(&(retval), (__force typeof(retval) __user *)(addr), sizeof(retval)); \
pagefault_enable(); \
set_fs(old_fs); \
ret; \
})
/*
* probe_kernel_read(): safely attempt to read from a location
* @dst: pointer to the buffer that shall take the data
@ -131,4 +101,14 @@ extern long notrace __probe_kernel_write(void *dst, const void *src, size_t size
extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
/**
* probe_kernel_address(): safely attempt to read from a location
* @addr: address to read from
* @retval: read into this variable
*
* Returns 0 on success, or -EFAULT.
*/
#define probe_kernel_address(addr, retval) \
probe_kernel_read(&retval, addr, sizeof(retval))
#endif /* __LINUX_UACCESS_H__ */

5
mm/maccess.c
View File

@ -13,6 +13,11 @@
*
* Safely read from address @src to the buffer at @dst. If a kernel fault
* happens, handle that and return -EFAULT.
*
* We ensure that the copy_from_user is executed in atomic context so that
* do_page_fault() doesn't attempt to take mmap_sem. This makes
* probe_kernel_read() suitable for use within regions where the caller
* already holds mmap_sem, or other locks which nest inside mmap_sem.
*/
long __weak probe_kernel_read(void *dst, const void *src, size_t size)