On Fri, Jan 26, 2018 at 05:03:29PM +0000, Ard Biesheuvel wrote: > On 26 January 2018 at 16:57, Will Deacon <will.deacon@xxxxxxx> wrote: > > On Thu, Jan 25, 2018 at 10:31:29AM +0000, Ard Biesheuvel wrote: > >> As a preparatory step towards unmapping the kernel entirely while > >> executing UEFI runtime services, move the stack and the entry > >> wrapper routine mappings into the EFI page tables. Also, create a > >> vector table that overrides the main one while executing in the > >> firmware so we will be able to remap/unmap the kernel while taking > >> interrupts. > > > > [...] > > > >> + .macro ventry > >> + .align 7 > >> +.Lv\@ : stp x29, x30, [sp, #-16]! // preserve x29 and x30 > >> + mrs x29, elr_el1 // preserve ELR > >> + adr x30, .Lret // take return address > >> + msr elr_el1, x30 // set ELR to return address > > > > Oh man, are you really doing two ERETs for a single exception, or am I > > missing something? > > > > Yes. I told you it was poetry. We should organise a recital. > >> + ldr x30, 2b // take address of 'vectors' > >> + msr vbar_el1, x30 // set VBAR to 'vectors' > >> + isb > >> + add x30, x30, #.Lv\@ - __efi_rt_vectors > >> + br x30 > >> + .endm > >> + > >> +.Lret: msr elr_el1, x29 > > > > If you take an IRQ here, aren't you toast? > > > > Yep. So we need to switch this with setting the VBAR below then. Hmm, but the ELR will still be clobbered by an IRQ, so I don't see how you can make this safe unless you hack SPSR before entering the kernel vectors on the entry side. > >> +__efi_rt_vectors: > >> + .rept 8 > >> + ventry > >> + .endr > > > > Have you thought about SDEI at all? I can't see any code here to handle > > that. > > > > Nope Add JamesM to cc ;) > >> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > >> index b34e717d7597..3bab6c60a12b 100644 > >> --- a/arch/arm64/kernel/entry.S > >> +++ b/arch/arm64/kernel/entry.S > >> @@ -204,6 +204,7 @@ alternative_if ARM64_HAS_PAN > >> alternative_else_nop_endif > >> > >> .if \el != 0 > >> + tbz x21, #63, 1f // skip if TTBR0 covers the stack > > > > So this is really a "detect EFI" check, right? Maybe comment it as such. > > Also, probably want to check bit 55 just in case tagging ever takes off. > > > > Right. So just bit #55 should be sufficient then, right? Yes, I think so. Will -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
