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 PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 13 Jun 2014 09:03:02 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Andy Lutomirski <luto@...capital.net> CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>, Russ Cox <rsc@...ang.org>, Ian Taylor <iant@...ang.org> Subject: Re: vdso feature requests from the Go people On 06/13/2014 08:34 AM, Andy Lutomirski wrote: > > I'm only aware of two implementations that work like that: glibc and > musl. AFAIK neither one even tries to use the vdso when statically > linked. IIRC, Bionic doesn't support the vdso at all, and Go has the > present issue. > I would expect uClibc to behave similarly. Bionic does, indeed, not support the vdso, but that is not for the lack of a linker but is really a shortcoming in Bionic. > And ELF parsing is a giant mess. Currently the vdso doesn't use > DT_GNU_HASH (easy to fix) but no one can safely rely on DT_GNU_HASH > being there, and DT_GNU_HASH isn't actually easier to parse. Right... and the vdso is small enough that the performance doesn't matter. However, we probably *ought* to publish DT_GNU_HASH data. >>> 2. Go uses a segmented stack, and the vdso is quite unfriendly for >>> segmented stack. If we can get compiler support, is there a >>> reasonable way that we could advertise the maximum stack usage of each >>> vdso entry point? >> >> I suspect an easier way to do that would just be to define a maximum >> stack usage for *any* vdso entry point, and then enable the gcc stack >> depth warning (perhaps even with Werror)... we can do this now. > > I can imagine this causing lots of pain when gcc 4.11 comes out with > some issue that blows up the stack usage. Or when akpm compiles on > Fedora Core 6 using some ancient toolchain that spills every local > variable three or four times and assigns every possible inline > function its own non-overlapping stack range. > > My copy of gcc supports -fstack-usage, which seems like an easyish way > to obtain the information. I'm not entirely sure whether > -fstack-usage refers to the whole call tree or just to the specific > function. There are issues either way. However, most vdso code doesn't use much stack at all, and it seems reasonable to put a (conservative) cap on it as a matter of policy. -hpa -- 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/
Powered by blists - more mailing lists