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authorJoerg Roedel <jroedel@suse.de>2020-10-28 17:46:58 +0100
committerBorislav Petkov <bp@suse.de>2020-10-29 18:09:59 +0100
commitc9f09539e16e281f92a27760fdfae71e8af036f6 (patch)
tree6e0eb9706062025102be18c76c366f339ce909ff /arch
parent86ce43f7dde81562f58b24b426cef068bd9f7595 (diff)
downloadlinux-stericsson-c9f09539e16e281f92a27760fdfae71e8af036f6.tar.gz
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')
-rw-r--r--arch/x86/kernel/head_64.S16
-rw-r--r--arch/x86/mm/mem_encrypt.c1
2 files changed, 17 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
/*
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index efbb3de472df..bc0833713be9 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -39,6 +39,7 @@
*/
u64 sme_me_mask __section(".data") = 0;
u64 sev_status __section(".data") = 0;
+u64 sev_check_data __section(".data") = 0;
EXPORT_SYMBOL(sme_me_mask);
DEFINE_STATIC_KEY_FALSE(sev_enable_key);
EXPORT_SYMBOL_GPL(sev_enable_key);