linux-kernel - Re: [PATCH v3 1/1] pgo: Fix allocate

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Date:   Fri, 4 Jun 2021 11:06:37 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jarmo Tiitto <jarmo.tiitto@...il.com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Bill Wendling <wcw@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        morbo@...gle.com
Subject: Re: [PATCH v3 1/1] pgo: Fix allocate_node() v2

On Fri, Jun 04, 2021 at 07:58:20PM +0300, Jarmo Tiitto wrote:
> When clang instrumentation eventually calls allocate_node()
> the struct llvm_prf_data *p argument tells us from what section
> we should reserve the vnode: It either points into vmlinux's
> core __llvm_prf_data section or some loaded module's
> __llvm_prf_data section.
> 
> But since we don't have access to corresponding
> __llvm_prf_vnds section(s) for any module, the function
> should return just NULL and ignore any profiling attempts
> from modules for now.
> 
> Signed-off-by: Jarmo Tiitto <jarmo.tiitto@...il.com>
> ---
> Based on Kees and others feedback here is v3 patch
> that clarifies why the current checks in allocate_node()
> are flawed. I did fair amount of KGDB time on it.
> 
> The commit is based on kees/for-next/clang/features tree,
> hopefully this is ok. Should I have based it on linux-next
> instead?
> 
> I grep -R'd where the memory_contains() can be found and it is only
> found in #include <asm-generic/sections.h>

That's true, but the way to use "asm-generic" is to include the
top-level "asm" file, so that architectures can override things as
needed.

> I cross my fingers and await if this is my first accepted patch. :-)

I tweaked it a bit and applied it (see the separate email).

Thank you!

-Kees

-- 
Kees Cook