Re: [PATCH] x86/asm/entry/32: Restore %ss before SYSRETL if necessary

[Borislav Petkov]

On Thu, Apr 23, 2015 at 10:01:16PM +0200, Denys Vlasenko wrote:
> Naturally, CS can't be NULL, and up until today
> I thought SS also can't. But the bit is probably implemented
> for all eight cached descriptors.

There's this section about NULL selector in APM v2. It says that NULL
selectors are used to invalidate segment registers and software can load
a NULL selector in SS in CPL0.

So, if an interrupt happens and as you quoted earlier that SS gets set
to NULL as a result of an interrupt, there's that SS leak causing the SS
exception.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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