Messages in this thread | | | Date | Fri, 11 Aug 2023 20:05:28 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86/retpoline: Don't clobber RFLAGS during srso_safe_ret() |
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On Fri, Aug 11, 2023 at 08:52:55AM -0700, Sean Christopherson wrote: > A major motivation for doing fast emulation is to leverage the CPU to > handle consumption and manipulation of arithmetic flags, i.e. RFLAGS is > both an input and output to the target of the call. fastop() collects > the RFLAGS result by pushing RFLAGS onto the stack and popping them back > into a variable (held in RDI in this case) > > asm("push %[flags]; popf; " CALL_NOSPEC " ; pushf; pop %[flags]\n"
Right, and I've tested this countless times with gcc-built host and guest.
But Nathan's case where the host is built with gcc but the guest with clang, would trigger this. And as he confirms, that fixes it so I wonder what is the difference in code generation to make this rFLAGS corruption noticeable in that particular configuration.
Oh well, later when the fires are put out.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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