exec: Call kmap_local_page() in copy_string_kernel()

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

diff --git a/fs/exec.c b/fs/exec.c
index 0fc56c70c870f0f9e3550a26bbc79d28796b2572..7e842d1bcb67489b9c79f3ca94469bef706b5f2e 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -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);
        }