linux-kernel - Re: [RFC 2/2] arm64: compat: cacheflush syscall: process only pages that are in the memory

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: <20180126174145.6gtfjjoxb57d7qwt@armageddon.cambridge.arm.com>
Date:   Fri, 26 Jan 2018 17:41:45 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Will Deacon <will.deacon@....com>,
        Inki Dae <inki.dae@...sung.com>,
        Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [RFC 2/2] arm64: compat: cacheflush syscall: process only pages
 that are in the memory

On Fri, Jan 26, 2018 at 12:14:41PM +0100, Marek Szyprowski wrote:
> @@ -32,23 +33,36 @@
>  static long
>  __do_compat_cache_op(unsigned long start, unsigned long end)
[...]
> +		if (follow_page(vma, start, 0)) {
> +			ret = __flush_cache_user_range(start, start + chunk);
> +			if (ret)
> +				goto done;
> +		}

This looks pretty expensive for pages already in memory. Could we do
some tricks with the AT instruction in __flush_cache_user_range() so
that we skip the flushing if the page isn't there? We know that when a
page is mapped, the cache will get cleaned/invalidated via set_pte_at()
+ sync_icache_dcache(), so the only problem of a race is flushing the
caches twice for a page. If a page gets unmapped after AT, we may bring
it back through the cache ops.

-- 
Catalin