linux-kernel - Re: [patches] RE: [PATCH 3/4] RISC-V: Flush I$ when making a dirty page executable

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <mhng-55eb51de-8c76-4dd1-b699-5ce082ed0dd2@palmer-si-x1c4>
Date:   Wed, 22 Nov 2017 09:38:16 -0800 (PST)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     David.Laight@...LAB.COM
CC:     linux-kernel@...r.kernel.org, patches@...ups.riscv.org,
        Andrew Waterman <andrew@...ive.com>
Subject:     Re: [patches] RE: [PATCH 3/4] RISC-V: Flush I$ when making a dirty page executable

On Tue, 21 Nov 2017 08:57:07 PST (-0800), David.Laight@...LAB.COM wrote:
> From: Palmer Dabbelt
>> Sent: 20 November 2017 18:58
>>
>> The RISC-V ISA allows for instruction caches that are not coherent WRT
>> stores, even on a single hart.  As a result, we need to explicitly flush
>> the instruction cache whenever marking a dirty page as executable in
>> order to preserve the correct system behavior.
>
> Isn't the I-flush only needed if there has been an unmap since the
> previous I-flush?
> Since code is rarely unmapped (exec and driver unload come to mind)
> the I-flush won't be needed very often.

There's nothing in the RISC-V ISA that prevents the instruction cache from 
caching read-only (or even unmapped!) pages.  Instructions fetched this manner 
could never commit, but they could fill up the icache with garbage.  I believe 
that means we need to flush on dirty->execute, but if I'm wrong I'm happy to 
change it.