[PATCH] fs: Call kmap_local_page() in copy_string_kernel()

From: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To: Benjamin LaHaise <bcrl@kvack.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Eric Biederman <ebiederm@xmission.com>,
	Kees Cook <keescook@chromium.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
	Jeff Layton <jlayton@kernel.org>,
	Chuck Lever <chuck.lever@oracle.com>,
	Jens Axboe <axboe@kernel.dk>,
	Pavel Begunkov <asml.silence@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Tom Rix <trix@redhat.com>,
	linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	nvdimm@lists.linux.dev, io-uring@vger.kernel.org,
	linux-riscv@lists.infradead.org, llvm@lists.linux.dev
Cc: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
	Ira Weiny <ira.weiny@intel.com>
Subject: [PATCH] fs: Call kmap_local_page() in copy_string_kernel()
Date: Sun, 10 Jul 2022 12:01:36 +0200	[thread overview]
Message-ID: <20220710100136.25496-1-fmdefrancesco@gmail.com> (raw)

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, not
globally visible and can take page faults. Furthermore, the mappings can be
acquired from any context (including interrupts).

Therefore, use kmap_local_page() in copy_string_kernel() instead of
kmap_atomic().

Tested with xfstests on a QEMU + KVM 32-bits VM booting a kernel with
HIGHMEM64GB enabled.

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---

I sent a first patch to fs/exec.c for converting kmap() and kmap_atomic()
to kmap_local_page():
https://lore.kernel.org/lkml/20220630163527.9776-1-fmdefrancesco@gmail.com/

Some days ago, Ira Weiny, while he was reviewing that patch, made me notice
that I had overlooked a second kmap_atomic() in the same file (thanks):
https://lore.kernel.org/lkml/YsiQptk19txHrG4c@iweiny-desk3/

I've been asked to send this as an additional change. This is why there will
not be any second version of that previous patch.

 fs/exec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 4a2129c0d422..5fa652ca5823 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -639,11 +639,11 @@ 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);
+		kaddr = kmap_local_page(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);
+		kunmap_local(kaddr);
 		put_arg_page(page);
 	}
 
-- 
2.36.1


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