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| author | Joerg Roedel <jroedel@suse.de> | 2020-10-28 17:46:58 +0100 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2020-10-29 18:09:59 +0100 |
| commit | c9f09539e16e281f92a27760fdfae71e8af036f6 (patch) | |
| tree | 6e0eb9706062025102be18c76c366f339ce909ff /arch/x86/kernel/head_64.S | |
| parent | 86ce43f7dde81562f58b24b426cef068bd9f7595 (diff) | |
| download | linux-c9f09539e16e281f92a27760fdfae71e8af036f6.tar.bz2 | |
x86/head/64: Check SEV encryption before switching to kernel page-table
When SEV is enabled, the kernel requests the C-bit position again from
the hypervisor to build its own page-table. Since the hypervisor is an
untrusted source, the C-bit position needs to be verified before the
kernel page-table is used.
Call sev_verify_cbit() before writing the CR3.
[ 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/20201028164659.27002-5-joro@8bytes.org
Diffstat (limited to 'arch/x86/kernel/head_64.S')
| -rw-r--r-- | arch/x86/kernel/head_64.S | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 7eb2a1c87969..3c417734790f 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -161,6 +161,21 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) /* Setup early boot stage 4-/5-level pagetables. */ addq phys_base(%rip), %rax + + /* + * For SEV guests: Verify that the C-bit is correct. A malicious + * hypervisor could lie about the C-bit position to perform a ROP + * attack on the guest by writing to the unencrypted stack and wait for + * the next RET instruction. + * %rsi carries pointer to realmode data and is callee-clobbered. Save + * and restore it. + */ + pushq %rsi + movq %rax, %rdi + call sev_verify_cbit + popq %rsi + + /* Switch to new page-table */ movq %rax, %cr3 /* Ensure I am executing from virtual addresses */ @@ -279,6 +294,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) SYM_CODE_END(secondary_startup_64) #include "verify_cpu.S" +#include "sev_verify_cbit.S" #ifdef CONFIG_HOTPLUG_CPU /* |