linux-kernel - Re: [PATCH] objtool: Documentation: document UACCESS warnings

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Message-Id: <90c16f02-9364-651e-6dea-8758a698d2ce@linux.vnet.ibm.com>
Date:   Tue, 24 Mar 2020 14:11:13 +0530
From:   Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>, jpoimboe@...hat.com,
        peterz@...radead.org
Cc:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Wolfram Sang <wsa@...-dreams.de>,
        Raphael Gault <raphael.gault@....com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] objtool: Documentation: document UACCESS warnings

On 3/24/20 5:43 AM, Nick Desaulniers wrote:
> Compiling with Clang and CONFIG_KASAN=y was exposing a few warnings:
>   call to memset() with UACCESS enabled
> 
> Document how to fix these for future travelers.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/876
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Looks good, a minor nitpick below.

> ---
>  .../Documentation/stack-validation.txt        | 20 +++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt
> index de094670050b..156fee13ba02 100644
> --- a/tools/objtool/Documentation/stack-validation.txt
> +++ b/tools/objtool/Documentation/stack-validation.txt
> @@ -289,6 +289,26 @@ they mean, and suggestions for how to fix them.
>        might be corrupt due to a gcc bug.  For more details, see:
>        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
> 
> +9. file.o: warning: objtool: funcA() call to funcB() with UACCESS enabled
> +
> +   This means that an unexpected call to a non-whitelisted function exists
> +   outside of arch-specific guards.
> +   X86: SMAP (stac/clac): __uaccess_begin()/__uaccess_end()
> +   ARM: PAN: uaccess_enable()/uaccess_enable()
                                 ^^^^^^ 
                                uaccess_disable() 

> +
> +   These functions should called to denote a minimal critical section around
> +   access to __user variables. See also: https://lwn.net/Articles/517475/

-- 
Kamalesh