On Thu, Feb 22, 2018 at 09:31:41AM -0600, Eric Sandeen wrote: > On 2/22/18 9:09 AM, Christoph Hellwig wrote: > > On Wed, Feb 21, 2018 at 06:16:25PM -0800, Darrick J. Wong wrote: > >> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > >> > >> Detect and enable retpolines for all code, to mitigate Spectre v2 > >> (branch target injection) on x86. > > > > The mechanics look ok, but why do we really care for xfsprogs? > > fs utilities seem like a lesser target and should just be covered They're a smaller target than the kernel, for sure, but the scary part about spectre is that unprivileged programs running on the same core as a privileged xfs_repair can then use branch predictor poisoning to cause problems with the xfs_repair. > > by hopefully sane compiler defaults, shouldn't they? I would have thought so, but look at the gcc manpage: -mindirect-branch=choice Convert indirect call and jump with choice. The default is keep, which keeps indirect call and jump unmodified. thunk Unmodified, as in don't provide spectre mitigations... converts indirect call and jump to call and return thunk. thunk-inline converts indirect call and jump to inlined call and return thunk. thunk-extern converts indirect call and jump to external call and return thunk provided in a separate object file. You can control this behavior for a specific function by using the function attribute "indirect_branch". Note that -mcmodel=large is incompatible with -mindirect-branch=thunk nor -mindirect-branch=thunk-extern since the thunk function may not be reachable in large code model. So, gcc defaults to unprotected. > That's my feeling as well - does manually fixing one utility out of > hundreds on the system help anything? Shouldn't this be done via toolchain > or distro-package-build defaults? Maybe they will someday, but right now: $ dpkg-buildflags --get CFLAGS -g -O2 -fdebug-prefix-map=/home/djwong=. -fstack-protector-strong -Wformat -Werror=format-security It's not clear to me if Debian plans to adopt the per-platform spectre mitigations distro-wide or just for specific packages, or what? So far it looks like Ubuntu is only doing it for their browser packages. libc hasn't been rebuilt, which limits the effectiveness of turning it on for xfsprogs, but otoh we could still protect the bits we control. --D > -Eric > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
