86ce43f7dd
Check whether the hypervisor reported the correct C-bit when running as an SEV guest. Using a wrong C-bit position could be used to leak sensitive data from the guest to the hypervisor. The check function is in a separate file: arch/x86/kernel/sev_verify_cbit.S so that it can be re-used in the running kernel image. [ bp: Massage. ] Signed-off-by: Joerg Roedel <jroedel@suse.de> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> Link: https://lkml.kernel.org/r/20201028164659.27002-4-joro@8bytes.org
90 lines
2.4 KiB
ArmAsm
90 lines
2.4 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0-only */
|
|
/*
|
|
* sev_verify_cbit.S - Code for verification of the C-bit position reported
|
|
* by the Hypervisor when running with SEV enabled.
|
|
*
|
|
* Copyright (c) 2020 Joerg Roedel (jroedel@suse.de)
|
|
*
|
|
* sev_verify_cbit() is called before switching to a new long-mode page-table
|
|
* at boot.
|
|
*
|
|
* Verify that the C-bit position is correct by writing a random value to
|
|
* an encrypted memory location while on the current page-table. Then it
|
|
* switches to the new page-table to verify the memory content is still the
|
|
* same. After that it switches back to the current page-table and when the
|
|
* check succeeded it returns. If the check failed the code invalidates the
|
|
* stack pointer and goes into a hlt loop. The stack-pointer is invalidated to
|
|
* make sure no interrupt or exception can get the CPU out of the hlt loop.
|
|
*
|
|
* New page-table pointer is expected in %rdi (first parameter)
|
|
*
|
|
*/
|
|
SYM_FUNC_START(sev_verify_cbit)
|
|
#ifdef CONFIG_AMD_MEM_ENCRYPT
|
|
/* First check if a C-bit was detected */
|
|
movq sme_me_mask(%rip), %rsi
|
|
testq %rsi, %rsi
|
|
jz 3f
|
|
|
|
/* sme_me_mask != 0 could mean SME or SEV - Check also for SEV */
|
|
movq sev_status(%rip), %rsi
|
|
testq %rsi, %rsi
|
|
jz 3f
|
|
|
|
/* Save CR4 in %rsi */
|
|
movq %cr4, %rsi
|
|
|
|
/* Disable Global Pages */
|
|
movq %rsi, %rdx
|
|
andq $(~X86_CR4_PGE), %rdx
|
|
movq %rdx, %cr4
|
|
|
|
/*
|
|
* Verified that running under SEV - now get a random value using
|
|
* RDRAND. This instruction is mandatory when running as an SEV guest.
|
|
*
|
|
* Don't bail out of the loop if RDRAND returns errors. It is better to
|
|
* prevent forward progress than to work with a non-random value here.
|
|
*/
|
|
1: rdrand %rdx
|
|
jnc 1b
|
|
|
|
/* Store value to memory and keep it in %rdx */
|
|
movq %rdx, sev_check_data(%rip)
|
|
|
|
/* Backup current %cr3 value to restore it later */
|
|
movq %cr3, %rcx
|
|
|
|
/* Switch to new %cr3 - This might unmap the stack */
|
|
movq %rdi, %cr3
|
|
|
|
/*
|
|
* Compare value in %rdx with memory location. If C-bit is incorrect
|
|
* this would read the encrypted data and make the check fail.
|
|
*/
|
|
cmpq %rdx, sev_check_data(%rip)
|
|
|
|
/* Restore old %cr3 */
|
|
movq %rcx, %cr3
|
|
|
|
/* Restore previous CR4 */
|
|
movq %rsi, %cr4
|
|
|
|
/* Check CMPQ result */
|
|
je 3f
|
|
|
|
/*
|
|
* The check failed, prevent any forward progress to prevent ROP
|
|
* attacks, invalidate the stack and go into a hlt loop.
|
|
*/
|
|
xorq %rsp, %rsp
|
|
subq $0x1000, %rsp
|
|
2: hlt
|
|
jmp 2b
|
|
3:
|
|
#endif
|
|
/* Return page-table pointer */
|
|
movq %rdi, %rax
|
|
ret
|
|
SYM_FUNC_END(sev_verify_cbit)
|