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Re: Revisiting x32 ABI state

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On Sun, 2018-02-11 at 10:56 +0100, Bastian Blank wrote:
> Moin
> 
> After almost four years and due to recent changes in the syscall path,
> I'd like to revisit our current handling of the x32 ABI.
> 
> Currently we disable support for the x32 ABI on runtime, enabling it
> needs a kernel command line parameter.  This Debian specific change was
> done due to concerns of ABI specific problems with the pretty new code.
> 
> In 4.15.2 the syscall path was cleaned up.  The so called "fast-path"
> was dropped completely, it didn't provide much of a fast path anymore
> because of the whole Spectre and Meltdown stuff.  Also our patch made
> inline patches of the fast path, to remove the overhead of the checks.
> 
> I think after that four years we shoud revisit that change.  Do we still
> think x32 may be a problem?

Yes, I think so.  Some people try to sandbox applications with syscall
blacklists that don't take x32 into account.  This is obviously a bad
idea since new syscalls are constantly being added, but that's the
reality we have to work with.

> Does the patch introduce runtime latency due to it's not longer
> inline patched form?

Yes, a little.  Maybe I should update the slow path to use a static
key.

Ben.

-- 
Ben Hutchings
Sturgeon's Law: Ninety percent of everything is crap.

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Revisiting x32 ABI state Bastian Blank <waldi@debian.org> - 2018-02-11 11:20 +0100
  Re: Revisiting x32 ABI state Ben Hutchings <ben@decadent.org.uk> - 2018-02-11 23:30 +0100

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