From: David Laight <David.Laight@ACULAB.COM>
To: 'Eric Biggers' <ebiggers3@gmail.com>,
Salvatore Mesoraca <s.mesoraca16@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>,
"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Herbert Xu <herbert@gondor.apana.org.au>,
"Kees Cook" <keescook@chromium.org>
Subject: RE: [PATCH] crypto: ctr: avoid VLA use
Date: Thu, 15 Mar 2018 11:55:21 +0000 [thread overview]
Message-ID: <913c28c268ca49f19f2407afc110deef@AcuMS.aculab.com> (raw)
In-Reply-To: <20180314183157.GA183724@gmail.com>
From: Eric Biggers
> Sent: 14 March 2018 18:32
...
> Also, I recall there being a long discussion a while back about how
> __aligned(16) doesn't work on local variables because the kernel's stack pointer
> isn't guaranteed to maintain the alignment assumed by the compiler (see commit
> b8fbe71f7535)...
ISTR that gcc arbitrarily decided that the x86 stack (for 32 bit) would be
kept aligned to more than 4 bytes (16??) - probably so that xmm registers
could be written to stack locations.
This was a massive ABI change that they didn't tell anyone about!
While gcc compiled code maintained the alignment a lot of asm code didn't.
I don't know about Linux, but NetBSD didn't even align user stacks.
There is a gcc option to not assume that the stack is 'appropriately aligned',
but ISTR that it generates rather more code that one might have wished.
If the compiler does align the stack, it does so by generating a double
stack frame - not pretty at all.
David
next prev parent reply other threads:[~2018-03-15 11:55 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-14 13:17 Salvatore Mesoraca
2018-03-14 13:31 ` Stephan Mueller
2018-03-14 13:46 ` Salvatore Mesoraca
2018-03-14 13:52 ` Stephan Mueller
2018-03-14 18:31 ` Eric Biggers
2018-03-14 19:25 ` Salvatore Mesoraca
2018-03-15 11:55 ` David Laight [this message]
2018-03-15 9:54 ` Herbert Xu
2018-03-15 10:42 ` Salvatore Mesoraca
2018-03-15 14:41 ` kbuild test robot
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