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exec: Call kmap_local_page() in copy_string_kernel()

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The use of kmap_atomic() is being deprecated in favor of kmap_local_page().

With kmap_local_page(), the mappings are per thread, CPU local and not
globally visible. Furthermore, the mappings can be acquired from any
context (including interrupts).

Therefore, replace kmap_atomic() with kmap_local_page() in
copy_string_kernel(). Instead of open-coding local mapping + memcpy(),
use memcpy_to_page(). Delete a redundant call to flush_dcache_page().

Tested with xfstests on a QEMU/ KVM x86_32 VM, 6GB RAM, booting a kernel
with HIGHMEM64GB enabled.

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220724212523.13317-1-fmdefrancesco@gmail.com
This commit is contained in:
Fabio M. De Francesco 2022-07-24 23:25:23 +02:00 committed by Kees Cook
parent 5036793d7d
commit c6e8e36c6a
1 changed files with 1 additions and 5 deletions
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6
fs/exec.c
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@ -631,7 +631,6 @@ int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
unsigned int bytes_to_copy = min_t(unsigned int, len,
min_not_zero(offset_in_page(pos), PAGE_SIZE));
struct page *page;
char *kaddr;
pos -= bytes_to_copy;
arg -= bytes_to_copy;
@ -640,11 +639,8 @@ int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
page = get_arg_page(bprm, pos, 1);
if (!page)
return -E2BIG;
kaddr = kmap_atomic(page);
flush_arg_page(bprm, pos & PAGE_MASK, page);
memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy);
flush_dcache_page(page);
kunmap_atomic(kaddr);
memcpy_to_page(page, offset_in_page(pos), arg, bytes_to_copy);
put_arg_page(page);
}