[PATCH v2 0/3] arm64: Enable BTI for the executable as well as the interpreter

[Mark Brown]

On Tue, Jun 15, 2021 at 04:22:06PM +0100, Dave Martin wrote:
> On Thu, Jun 10, 2021 at 11:28:12AM -0500, Jeremy Linton via Libc-alpha wrote:

> > Thus, I expect that with his patch applied to 5.13 the service will fail to
> > start regardless of the state of MDWE, but it seems to continue starting
> > when I set MDWE=yes. Same behavior with v1 FWTW.

> If the failure we're trying to detect is that BTI is undesirably left
> off for the main executable, surely replacing BTIs with NOPs will make
> no differenece?  The behaviour with PROT_BTI clear is strictly more
> permissive than with PROT_BTI set, so I'm not sure we can test the
> behaviour this way.

> Maybe I'm missing sometihng / confused myself somewhere.

The issue this patch series is intended to address is that BTI gets
left off since the dynamic linker is unable to enable PROT_BTI on the
main executable.  We're looking to see that we end up with the stricter
permissions checking of BTI, with the issue present landing pads
replaced by NOPs will not fault but once the issue is addressed they
should start faulting.

> Looking at /proc/<pid>/maps after the process starts up may be a more
> reliable approach, so see what the actual prot value is on the main
> executable's text pages.

smaps rather than maps but yes, executable pages show up as "ex" and BTI
adds a "bt" tag in VmFlags.
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