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uaccess: add force_uaccess_{begin,end} helpers

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Add helpers to wrap the get_fs/set_fs magic for undoing any damange done
by set_fs(KERNEL_DS).  There is no real functional benefit, but this
documents the intent of these calls better, and will allow stubbing the
functions out easily for kernels builds that do not allow address space
overrides in the future.

[hch@lst.de: drop two incorrect hunks, fix a commit log typo]
  Link: http://lkml.kernel.org/r/20200714105505.935079-6-hch@lst.de

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Greentime Hu <green.hu@gmail.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Nick Hu <nickhu@andestech.com>
Cc: Vincent Chen <deanbo422@gmail.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Link: http://lkml.kernel.org/r/20200710135706.537715-6-hch@lst.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Christoph Hellwig
2020-08-11 18:33:47 -07:00
committed by Linus Torvalds
parent 428e2976a5
commit 3d13f313ce
12 changed files with 63 additions and 56 deletions
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22
mm/maccess.c
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@@ -205,15 +205,14 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
{
long ret = -EFAULT;
mm_segment_t old_fs = get_fs();
mm_segment_t old_fs = force_uaccess_begin();
set_fs(USER_DS);
if (access_ok(src, size)) {
pagefault_disable();
ret = __copy_from_user_inatomic(dst, src, size);
pagefault_enable();
}
set_fs(old_fs);
force_uaccess_end(old_fs);
if (ret)
return -EFAULT;
@@ -233,15 +232,14 @@ EXPORT_SYMBOL_GPL(copy_from_user_nofault);
long copy_to_user_nofault(void __user *dst, const void *src, size_t size)
{
long ret = -EFAULT;
mm_segment_t old_fs = get_fs();
mm_segment_t old_fs = force_uaccess_begin();
set_fs(USER_DS);
if (access_ok(dst, size)) {
pagefault_disable();
ret = __copy_to_user_inatomic(dst, src, size);
pagefault_enable();
}
set_fs(old_fs);
force_uaccess_end(old_fs);
if (ret)
return -EFAULT;
@@ -270,17 +268,17 @@ EXPORT_SYMBOL_GPL(copy_to_user_nofault);
long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
long count)
{
mm_segment_t old_fs = get_fs();
mm_segment_t old_fs;
long ret;
if (unlikely(count <= 0))
return 0;
set_fs(USER_DS);
old_fs = force_uaccess_begin();
pagefault_disable();
ret = strncpy_from_user(dst, unsafe_addr, count);
pagefault_enable();
set_fs(old_fs);
force_uaccess_end(old_fs);
if (ret >= count) {
ret = count;
@@ -310,14 +308,14 @@ long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
*/
long strnlen_user_nofault(const void __user *unsafe_addr, long count)
{
mm_segment_t old_fs = get_fs();
mm_segment_t old_fs;
int ret;
set_fs(USER_DS);
old_fs = force_uaccess_begin();
pagefault_disable();
ret = strnlen_user(unsafe_addr, count);
pagefault_enable();
set_fs(old_fs);
force_uaccess_end(old_fs);
return ret;
}