From: Dmitry Vyukov <dvyukov@google.com>
To: Patricia Alfonso <trishalfonso@google.com>
Cc: Jeff Dike <jdike@addtoit.com>,
Richard Weinberger <richard@nod.at>,
anton.ivanov@cambridgegreys.com,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
David Gow <davidgow@google.com>,
Brendan Higgins <brendanhiggins@google.com>,
linux-um@lists.infradead.org,
kasan-dev <kasan-dev@googlegroups.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] UML: add support for KASAN under x86_64
Date: Thu, 16 Jan 2020 09:44:08 +0100 [thread overview]
Message-ID: <CACT4Y+bPzRbWw-dPQkLVENPKy_DBdjrbSce0f6XE3=W7RhfhBA@mail.gmail.com> (raw)
In-Reply-To: <20200115182816.33892-1-trishalfonso@google.com>
On Wed, Jan 15, 2020 at 7:28 PM Patricia Alfonso
<trishalfonso@google.com> wrote:
> +config KASAN_SHADOW_OFFSET
> + hex
> + depends on KASAN
> + default 0x100000000000
> + help
> + This is the offset at which the ~2.25TB of shadow memory is
> + initialized and used by KASAN for memory debugging. The default
> + is 0x100000000000.
What are restrictions on this value?
In user-space we use 0x7fff8000 as a base (just below 2GB) and it's
extremely profitable wrt codegen since it fits into immediate of most
instructions.
We can load and add the base with a short instruction:
2d8c: 48 81 c2 00 80 ff 7f add $0x7fff8000,%rdx
Or even add base, load shadow and check it with a single 7-byte instruction:
1e4: 80 b8 00 80 ff 7f 00 cmpb $0x0,0x7fff8000(%rax)
While with the large base, it takes 10 bytes just to load the const
into a register (current x86 KASAN codegen):
ffffffff81001571: 48 b8 00 00 00 00 00 fc ff df movabs
$0xdffffc0000000000,%rax
Most instructions don't have 8-byte immediates, so then we separately
need to add/load/check.
next prev parent reply other threads:[~2020-01-16 8:44 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-15 18:28 [RFC PATCH] UML: add support for KASAN under x86_64 Patricia Alfonso
2020-01-15 18:48 ` Johannes Berg
2020-01-15 22:56 ` Patricia Alfonso
2020-01-16 7:57 ` Johannes Berg
2020-01-16 8:03 ` Johannes Berg
2020-01-16 9:18 ` Dmitry Vyukov
2020-01-16 9:20 ` Johannes Berg
2020-01-16 9:23 ` Dmitry Vyukov
2020-01-17 9:59 ` Dmitry Vyukov
2020-01-17 10:03 ` Dmitry Vyukov
2020-01-17 10:05 ` Dmitry Vyukov
2020-02-06 18:33 ` Patricia Alfonso
2020-02-06 18:21 ` Patricia Alfonso
2020-02-06 19:14 ` Johannes Berg
2020-01-16 8:24 ` Dmitry Vyukov
2020-01-16 8:44 ` Dmitry Vyukov [this message]
2020-02-11 23:48 ` Patricia Alfonso
2020-02-12 6:23 ` Dmitry Vyukov
2020-01-16 8:50 ` Dmitry Vyukov
2020-01-16 8:52 ` Dmitry Vyukov
2020-02-12 0:19 ` Patricia Alfonso
2020-02-12 6:24 ` Dmitry Vyukov
2020-02-12 22:25 ` Patricia Alfonso
2020-02-13 5:39 ` Dmitry Vyukov
2020-02-13 22:55 ` Patricia Alfonso
2020-01-16 9:09 ` Dmitry Vyukov
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