From 0d7601e5467a710cbdda4edf88440dbb6a334b6e Mon Sep 17 00:00:00 2001 From: Tom Lendacky Date: Wed, 12 Aug 2020 15:21:42 -0500 Subject: UefiCpuPkg: Add a 16-bit protected mode code segment descriptor BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198 A hypervisor is not allowed to update an SEV-ES guests register state, so when booting an SEV-ES guest AP, the hypervisor is not allowed to set the RIP to the guest requested value. Instead, an SEV-ES AP must be transition from 64-bit long mode to 16-bit real mode in response to an INIT-SIPI-SIPI sequence. This requires a 16-bit code segment descriptor. For PEI, create this descriptor in the reset vector GDT table. For DXE, create this descriptor from the newly reserved entry at location 0x28. Cc: Eric Dong Cc: Ray Ni Cc: Laszlo Ersek Reviewed-by: Eric Dong Signed-off-by: Tom Lendacky Regression-tested-by: Laszlo Ersek --- UefiCpuPkg/ResetVector/Vtf0/Ia16/Real16ToFlat32.asm | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'UefiCpuPkg/ResetVector') diff --git a/UefiCpuPkg/ResetVector/Vtf0/Ia16/Real16ToFlat32.asm b/UefiCpuPkg/ResetVector/Vtf0/Ia16/Real16ToFlat32.asm index ce4ebfffb6..0e79a3984b 100644 --- a/UefiCpuPkg/ResetVector/Vtf0/Ia16/Real16ToFlat32.asm +++ b/UefiCpuPkg/ResetVector/Vtf0/Ia16/Real16ToFlat32.asm @@ -129,5 +129,14 @@ LINEAR_CODE64_SEL equ $-GDT_BASE DB 0 ; base 31:24 %endif +; linear code segment descriptor +LINEAR_CODE16_SEL equ $-GDT_BASE + DW 0xffff ; limit 15:0 + DW 0 ; base 15:0 + DB 0 ; base 23:16 + DB PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(CODE32_TYPE) + DB GRANULARITY_FLAG(1)|DEFAULT_SIZE32(0)|CODE64_FLAG(0)|UPPER_LIMIT(0xf) + DB 0 ; base 31:24 + GDT_END: -- cgit v1.2.3