On Thu, Jun 7, 2018 at 4:00 PM, Andy Lutomirski [off-list ref] wrote:

On Thu, Jun 7, 2018 at 3:03 PM H.J. Lu [off-list ref] wrote:

quoted

On Thu, Jun 7, 2018 at 1:50 PM, Andy Lutomirski [off-list ref] wrote:

quoted

On Thu, Jun 7, 2018 at 7:42 AM Yu-cheng Yu [off-list ref] wrote:

quoted

From: "H.J. Lu" <redacted>

When Intel indirect branch tracking is enabled, functions in vDSO which
may be called indirectly should have endbr32 or endbr64 as the first
instruction.  We try to compile vDSO with -fcf-protection=branch -mibt
if possible.  Otherwise, we insert endbr32 or endbr64 by hand to assembly
codes generated by the compiler.

Wow, that's... a genuine abomination.  Do we really need to support
CET on kernels built with old toolchains?

Yes.  GCC 7 should be able to build CET kernel.

Why?  Presumably people running distros that use CET are going to have
kernels build with a CET-supporting compiler.

Good point.  It was needed before GCC 8 was released.   We can drop
arch/x86/entry/vdso/endbr.sh now.

-- 
H.J.
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