Re: [PATCH] x86/entry_32: Move CLEAR_CPU_BUFFERS before CR3 switch
From: Dave Hansen
Date: Thu May 09 2024 - 20:36:34 EST
On 4/26/24 16:48, Pawan Gupta wrote:
> Move the VERW before the CR3 switch for 32-bit kernels as a workaround.
I look at the 32-bit code so rarely, I seem to forget have to re-learn
this gunk every time I look at it. Take a look at RESTORE_INT_REGS. On
32-bit, we actually restore %ds:
popl %ds
So even doing this:
> + CLEAR_CPU_BUFFERS
> /* Restore user state */
> RESTORE_REGS pop=4 # skip orig_eax/error_code
> - CLEAR_CPU_BUFFERS
> .Lirq_return:
fixes the issue. Moving it above the CR3 switch also works of course,
but I don't think this has anything to do with CR3. It's just that
userspace sets a funky %ds value and CLEAR_CPU_BUFFERS uses ds:.
I don't think any of the segment registers can have secrets in them, can
they? I mean, it's possible, but in practice I can't imagine.
So why not just do the CLEAR_CPU_BUFFERS in RESTORE_REGS but after
RESTORE_INT_REGS? You might be able to do it universally, or you could
pass in a macro argument to do it conditionally.
P.S. Can we remove 32-bit support yet? Please? :)