From: Al Viro <viro@zeniv.linux.org.uk>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Jann Horn <jannh@google.com>,
baloo@gandi.net, the arch/x86 maintainers <x86@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
kernel list <linux-kernel@vger.kernel.org>,
Pascal Bouchareine <pascal@gandi.net>
Subject: Re: [PATCH] x86: uaccess: fix regression in unsafe_get_user
Date: Sun, 17 Feb 2019 00:02:37 +0000 [thread overview]
Message-ID: <20190217000237.GQ2217@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20190216234702.GP2217@ZenIV.linux.org.uk>
On Sat, Feb 16, 2019 at 11:47:02PM +0000, Al Viro wrote:
> On Sat, Feb 16, 2019 at 02:50:15PM -0800, Andy Lutomirski wrote:
>
> > What is the actual problem? We’re not actually demand-faulting this data, are we? Are we just overrunning the buffer because the from_user helpers are too clever? Can we fix it for real by having the fancy helpers do *aligned* loads so that they don’t overrun the buffer? Heck, this might be faster, too.
>
> Unaligned _stores_ are not any cheaper, and you'd get one hell of
> extra arithmetics from trying to avoid both. Check something
> like e.g. memcpy() on alpha, where you really have to keep all
> accesses aligned, both on load and on store side.
>
> Can't we just pad the buffers a bit? Making sure that name_buf
> and symlink_buf are _not_ followed by unmapped pages shouldn't
> be hard. Both are allocated by kmalloc(), so...
>
> What am I missing here?
... the fact that read_info() might skip copying if everything it
wants is already in the buffer passed by decompressor ;-/ It's
been a while since I looked into that code...
next prev parent reply other threads:[~2019-02-17 0:02 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-15 23:59 [PATCH] x86: uaccess: fix regression in unsafe_get_user baloo
2019-02-16 4:20 ` Jann Horn
2019-02-16 20:18 ` Thomas Gleixner
2019-02-16 22:25 ` Thomas Gleixner
2019-02-16 22:50 ` Andy Lutomirski
2019-02-16 22:57 ` Andy Lutomirski
2019-02-16 23:47 ` Al Viro
2019-02-17 0:02 ` Al Viro [this message]
2019-02-17 2:36 ` Andy Lutomirski
2019-02-17 3:41 ` Arthur Gautier
2019-02-17 4:22 ` Al Viro
2019-02-18 13:04 ` Thomas Gleixner
2019-02-18 19:15 ` Andy Lutomirski
2019-02-18 21:13 ` Jann Horn
2019-02-18 21:51 ` Arthur Gautier
2019-09-26 9:58 ` Arthur Gautier
2019-09-26 14:09 ` Borislav Petkov
2019-10-10 16:49 ` Arthur Gautier
2019-11-05 14:11 ` Borislav Petkov
2019-11-05 16:05 ` Arthur Gautier
2019-11-06 0:21 ` Andy Lutomirski
2019-11-06 2:22 ` Arthur Gautier
2019-09-26 14:08 ` Borislav Petkov
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