linux-kernel - Re: 64-syscall args on 32-bit vs syscall()

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]

Date:	Tue, 16 Mar 2010 07:27:09 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	David Miller <davem@...emloft.net>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel@...savvy.com,
	drepper@...hat.com, torvalds@...ux-foundation.org,
	munroesj@...ux.vnet.ibm.com
Subject: Re: 64-syscall args on 32-bit vs syscall()

On Mon, 2010-03-15 at 14:44 +0100, Ralf Baechle wrote:
> Syscall is most often used for new syscalls that have no syscall stub in
> glibc yet, so the user of syscall() encodes this ABI knowledge.  If at a
> later stage syscall() is changed to have this sort of knowledge we break
> the API.  This is something only the kernel can get right. 

Well, no. The change I propose would not break the ABI on powerpc and
would auto-magically fix thoses cases :-) But again, you don't have to
do the same thing on MIPS or sparc, it's definitely arch specific.

IE. What you are saying is that a syscall defined in the kernel as:

	sys_foo(u64 arg);

To be called from userspace would require something like:

	u64 arg = 0x123456789abcdef01;

#if defined(__powerpc__) && WORDSIZE == 32
	syscall(SYS_foo, (u32)(arg >> 32), (u32)arg);
#ese
	syscall(SYS_foo, arg);

While with the trick of making syscall a macro wrapping an underlying
__syscall that has an added dummy argument, the register alignment is
"corrected" and thus -both- forms above suddenly work for me. That might
actually work for you too.

Cheers,
Ben.

--
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/