From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org, Jeremy Kerr <jk@ozlabs.org>,
linux-fsdevel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
"Eric W . Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH 8/8] exec: open code copy_string_kernel
Date: Sun, 19 Apr 2020 11:44:06 +0200 [thread overview]
Message-ID: <5f96e86a-b084-4330-b7d1-08b78416994c@c-s.fr> (raw)
In-Reply-To: <20200419080646.GE12222@lst.de>
Le 19/04/2020 à 10:06, Christoph Hellwig a écrit :
> On Sat, Apr 18, 2020 at 10:15:42AM +0200, Christophe Leroy wrote:
>>
>>
>> Le 14/04/2020 à 09:01, Christoph Hellwig a écrit :
>>> Currently copy_string_kernel is just a wrapper around copy_strings that
>>> simplifies the calling conventions and uses set_fs to allow passing a
>>> kernel pointer. But due to the fact the we only need to handle a single
>>> kernel argument pointer, the logic can be sigificantly simplified while
>>> getting rid of the set_fs.
>>
>>
>> Instead of duplicating almost identical code, can you write a function that
>> takes whether the source is from user or from kernel, then you just do
>> things like:
>>
>> if (from_user)
>> len = strnlen_user(str, MAX_ARG_STRLEN);
>> else
>> len = strnlen(str, MAX_ARG_STRLEN);
>>
>>
>> if (from_user)
>> copy_from_user(kaddr+offset, str, bytes_to_copy);
>> else
>> memcpy(kaddr+offset, str, bytes_to_copy);
>
> We'll need two different str variables then with and without __user
> annotations to keep type safety. And introduce a branch-y and unreadable
> mess in the exec fast path instead of adding a simple and well understood
> function for the kernel case that just deals with the much simpler case
> of just copying a single arg vector from a kernel address.
>
About the branch, I was expecting GCC to inline and eliminate the unused
branch.
next prev parent reply other threads:[~2020-04-19 9:44 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 7:01 remove set_fs calls from the exec and coredump code v2 Christoph Hellwig
2020-04-14 7:01 ` [PATCH 1/8] powerpc/spufs: simplify spufs core dumping Christoph Hellwig
2020-04-14 7:01 ` [PATCH 2/8] signal: clean up __copy_siginfo_to_user32 Christoph Hellwig
2020-04-17 21:08 ` Eric W. Biederman
2020-04-17 21:09 ` [PATCH 1/2] signal: Factor copy_siginfo_to_external32 from copy_siginfo_to_user32 Eric W. Biederman
2020-04-18 8:05 ` Christophe Leroy
2020-04-18 11:55 ` Eric W. Biederman
2020-04-19 8:13 ` Christoph Hellwig
2020-04-19 9:46 ` Christophe Leroy
2020-04-19 9:54 ` Christophe Leroy
2020-04-19 8:05 ` Christoph Hellwig
2020-04-17 21:09 ` [PATCH 2/2] signal: Remove the set_fs in binfmt_elf.c:fill_siginfo_note Eric W. Biederman
2020-04-19 8:03 ` [PATCH 2/8] signal: clean up __copy_siginfo_to_user32 Christoph Hellwig
2020-04-14 7:01 ` [PATCH 3/8] signal: replace __copy_siginfo_to_user32 with to_compat_siginfo Christoph Hellwig
2020-04-14 14:00 ` Arnd Bergmann
2020-04-14 7:01 ` [PATCH 4/8] binfmt_elf: open code copy_siginfo_to_user to kernelspace buffer Christoph Hellwig
2020-04-14 13:15 ` Arnd Bergmann
2020-04-15 7:45 ` Christoph Hellwig
2020-04-15 8:20 ` Arnd Bergmann
2020-04-17 13:27 ` Christoph Hellwig
2020-04-17 18:10 ` Eric W. Biederman
2020-04-17 20:06 ` Arnd Bergmann
2020-04-15 3:01 ` Michael Ellerman
2020-04-15 6:19 ` Christoph Hellwig
2020-04-14 7:01 ` [PATCH 5/8] binfmt_elf: remove the set_fs(KERNEL_DS) in elf_core_dump Christoph Hellwig
2020-04-14 7:01 ` [PATCH 6/8] binfmt_elf_fdpic: remove the set_fs(KERNEL_DS) in elf_fdpic_core_dump Christoph Hellwig
2020-04-14 7:01 ` [PATCH 7/8] exec: simplify the copy_strings_kernel calling convention Christoph Hellwig
2020-04-14 7:01 ` [PATCH 8/8] exec: open code copy_string_kernel Christoph Hellwig
2020-04-18 8:15 ` Christophe Leroy
2020-04-19 8:06 ` Christoph Hellwig
2020-04-19 9:44 ` Christophe Leroy [this message]
2020-04-17 22:41 ` remove set_fs calls from the exec and coredump code v2 Eric W. Biederman
2020-04-19 8:19 ` Christoph Hellwig
2020-04-19 11:50 ` Eric W. Biederman
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