From: rishabhb@codeaurora.org
To: keescook@chromium.org, linux-kernel@vger.kernel.org,
linux-arm-msm@vger.kernel.org,
Linux-arm Kernel <linux-arm-kernel@lists.infradead.org>
Cc: tsoni@codeaurora.org, ckadabi@codeaurora.org
Subject: usercopy_warn in __copy_to_user
Date: Wed, 19 Dec 2018 11:51:19 -0800 [thread overview]
Message-ID: <ecb306ea6f4a83302e78884713ad7823@codeaurora.org> (raw)
In the 4.19 kernel, we are seeing a USERCOPY_WARN in __copy_to_user
during bootup.
The code-flow is something like this:
(arch/arm64/kernel/signal.c)
struct sigset_t *set;
__copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set))
(include/linux/uaccess.h)
__copy_to_user(void __user *to, const void *from, unsigned long n)
{
might_fault();
kasan_check_read(from, n);
check_object_size(from, n, true);
return raw_copy_to_user(to, from, n);
}
(include/linux/thread_info.h)
static __always_inline void check_object_size(const void *ptr,
unsigned long n, bool to_user)
{
if (!__builtin_constant_p(n))
__check_object_size(ptr, n, to_user);
}
Since sizeof(*set) is constant, __builtin_constant_p(n) should return
true.
But we are seeing that its returning the value as false. Because of
which
the code goes on to __check_object_size and generates a USERCOPY_WARN
("usercopy: WARN() on slab cache usercopy
region violations").
We are using LLVM clang version 6.0 to compile the kernel and not gcc.
In clang, __builtin_constant_p is evaluated immediately, before inlining
or other optimizations run, gcc evaluates it later.
We believe that maybe causing __builtin_constant_p(n) to return false.
There’s upstream work to change LLVM, so __builtin_constant_p works more
like gcc when optimization is enabled, but its still in progress.
For this scenario is there a way to avoid the warning? Should the code
be
written in a different to avoid dependency on compiler?
Thanks,
Rishabh
next reply other threads:[~2018-12-19 19:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-19 19:51 rishabhb [this message]
2018-12-19 21:51 ` usercopy_warn in __copy_to_user Kees Cook
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ecb306ea6f4a83302e78884713ad7823@codeaurora.org \
--to=rishabhb@codeaurora.org \
--cc=ckadabi@codeaurora.org \
--cc=keescook@chromium.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-arm-msm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=tsoni@codeaurora.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).