On 8/27/2020 7:08 AM, H.J. Lu wrote:

On Thu, Aug 27, 2020 at 7:07 AM H.J. Lu [off-list ref] wrote:

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On Thu, Aug 27, 2020 at 6:36 AM Florian Weimer [off-list ref] wrote:

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* H. J. Lu:

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On Thu, Aug 27, 2020 at 6:19 AM Florian Weimer [off-list ref] wrote:

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* Dave Martin:

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You're right that this has implications: for i386, libc probably pulls
more arguments off the stack than are really there in some situations.
This isn't a new problem though.  There are already generic prctls with
fewer than 4 args that are used on x86.

As originally posted, glibc prctl would have to know that it has to pull
an u64 argument off the argument list for ARCH_X86_CET_DISABLE.  But
then the u64 argument is a problem for arch_prctl as well.

Argument of ARCH_X86_CET_DISABLE is int and passed in register.

The commit message and the C source say otherwise, I think (not sure
about the C source, not a kernel hacker).

It should read:

arch_prctl(ARCH_X86_CET_DISABLE, unsigned long features)

Or

arch_prctl(ARCH_X86_CET_DISABLE, unsigned int features)

Like other arch_prctl()'s, this parameter was 'unsigned long' earlier. 
The idea was, since this arch_prctl is only implemented for the 64-bit 
kernel, we wanted it to look as 64-bit only.  I will change it back to 
'unsigned long'.

Yu-cheng