linux-kernel - Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

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Message-ID: <eb7fdc6b-889f-4934-814f-f0572f4b089a@csgroup.eu>
Date: Thu, 29 Aug 2024 20:50:28 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Segher Boessenkool <segher@...nel.crashing.org>
Cc: Ard Biesheuvel <ardb@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 "Jason A . Donenfeld" <Jason@...c4.com>, Eric Biggers <ebiggers@...nel.org>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Naveen N Rao <naveen@...nel.org>, Andy Lutomirski <luto@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Theodore Ts'o <tytso@....edu>, Andrew Morton <akpm@...ux-foundation.org>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Vincenzo Frascino <vincenzo.frascino@....com>, shuah <shuah@...nel.org>,
 linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, Linux-Arch <linux-arch@...r.kernel.org>,
 linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

Le 29/08/2024 à 20:02, Segher Boessenkool a écrit :
> On Thu, Aug 29, 2024 at 07:36:38PM +0200, Christophe Leroy wrote:
>>
>>
>> Le 28/08/2024 à 19:25, Segher Boessenkool a écrit :
>>>
>>>> Not sure about static binaries, though: do those even use the VDSO?
>>>
>>> With "static binary" people usually mean "a binary not using any DSOs",
>>> I think the VDSO is a DSO, also in this respect?  As always, -static
>>> builds are *way* less problematic (and faster and smaller :-) )
>>>
>>
>> AFAIK on powerpc even static binaries use the vDSO, otherwise signals
>> don't work.
> 
> How can that work?  Non-dynamic binaries do not use ld.so (that is the
> definition of a dynamic binary, even).  So they cannot link (at runtime)
> to any DSO (unless that is done manually?!)
> 
> Maybe there is something at a fixed offset in the vDSO, or something
> like that?  Is this documented somewhere?
> 

You've got some explanation here : 
https://github.com/torvalds/linux/blob/master/Documentation/ABI/stable/vdso