linux-kernel - Re: [PATCH 3/3] um: Implement a x86

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] [day] [month] [year] [list]

Message-ID: <CAObL_7Gss0GcB8OtoCf-rUdsi8n4345gBESBub+5hu4g9fcssw@mail.gmail.com>
Date:	Wed, 20 Jul 2011 14:19:13 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Richard Weinberger <richard@....at>
Cc:	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] um: Implement a x86_64 vDSO

On Wed, Jul 20, 2011 at 2:09 PM, Richard Weinberger <richard@....at> wrote:
> Am Mittwoch 20 Juli 2011, 19:54:02 schrieb Andy Lutomirski:
>> On 07/18/2011 09:07 AM, Richard Weinberger wrote:
>> > Until now UML had no x86_64 vDSO.
>> > So glibc always used the vsyscall page for gettimeday()
>> > and friends.
>> > Calls to gettimeday() returned falsely the host time and
>> > confused some programs.
>> >
>> > This patch adds a vDSO which turns all __vdso_* calls into
>> > a system call so that UML can trap them.
>> >
>> > As glibc still uses the vsyscall page for static binaries this
>> > patch improves the situation only for dynamic binaries.
>> >
>> > Signed-off-by: Richard Weinberger<richard@....at>
>> >
>> > +   asm("syscall" : "=a" (ret) :
>> > +           "0" (__NR_clock_gettime), "D" (clock), "S" (ts) : "memory");
>> > +
>>
>> The x86-64 ABI and glibc think that rcx, and r11 are clobbered.  glibc
>> also thinks that cc is clobbered.  I personally think that rdx and
>> r8-r15 ought to be clobbered under the principle that syscall should
>> look like a function call.
>
> Hmm, I thought my implementation is fine because it follows
> arch/x86/vdso/vclock_gettime.c (Linus' tree).
>
> notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
> {
>  long ret;
>  asm("syscall" : "=a" (ret) :
>      "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
>  return ret;
> }
>
> Am I missing something or needs vdso_fallback_gettime() also some updates?

vdso_fallback_gettime is going away :)

I haven't read all of the sysret code paths, but it looks like at
least r11 is used in a comment.  That being said, your code is an
uninlinable function, and functions already clobber all those
registers, so the code shouldn't cause problems in real life.

--Andy
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/