Before this commit, KVM-Unit-Tests set up process crashes when executing
'lgdt' instruction under SEV-ES. This is because lgdt triggers UEFI
procedures (e.g. UEFI #VC handler) that require UEFI's code and data
segments. But these segments are are not compatible with KVM-Unit-Tests
GDT:
UEFI uses 0x30 as code segment and 0x38 as data segment, but in
KVM-Unit-Tests' GDT, 0x30 is a data segment, and 0x38 is a code segment.
This discrepancy crashes the UEFI procedures and thus crashes the 'lgdt'
execution.
This commit fixes this issue by copying UEFI GDT's code and data
segments into KVM-Unit-Tests GDT, so that UEFI procedures (e.g. UEFI #VC
handler) can work.
In this commit, the guest VM passes setup_gdt_tss() but crashes in
load_idt(), which will be fixed by follow-up commits.
Signed-off-by: Zixuan Wang <zixuanwang@xxxxxxxxxx>
---
lib/x86/amd_sev.c | 41 +++++++++++++++++++++++++++++++++++++++++
lib/x86/amd_sev.h | 1 +
lib/x86/setup.c | 4 ++++
3 files changed, 46 insertions(+)
diff --git a/lib/x86/amd_sev.c b/lib/x86/amd_sev.c
index 8d4df8c..c9fabc4 100644
--- a/lib/x86/amd_sev.c
+++ b/lib/x86/amd_sev.c
@@ -91,6 +91,47 @@ bool amd_sev_es_enabled(void)
return sev_es_enabled;
}
+static void copy_gdt_entry(gdt_entry_t *dst, gdt_entry_t *src, unsigned segment)
+{
+ unsigned index;
+
+ index = segment / sizeof(gdt_entry_t);
+ dst[index] = src[index];
+}
+
+/* Defined in x86/efi/efistart64.S */
+extern gdt_entry_t gdt64[];
+
+/*
+ * Copy UEFI's code and data segments to KVM-Unit-Tests GDT.
+ *
+ * This is because KVM-Unit-Tests reuses UEFI #VC handler that requires UEFI
+ * code and data segments to run. The UEFI #VC handler crashes the guest VM if
+ * these segments are not available. So we need to copy these two UEFI segments
+ * into KVM-Unit-Tests GDT.
+ *
+ * UEFI uses 0x30 as code segment and 0x38 as data segment. Fortunately, these
+ * segments can be safely overridden in KVM-Unit-Tests as they are used as
+ * protected mode and real mode segments (see x86/efi/efistart64.S for more
+ * details), which are not used in EFI set up process.
+ */
+void copy_uefi_segments(void)
+{
+ if (!amd_sev_es_enabled()) {
+ return;
+ }
+
+ /* GDT and GDTR in current UEFI */
+ gdt_entry_t *gdt_curr;
+ struct descriptor_table_ptr gdtr_curr;
+
+ /* Copy code and data segments from UEFI */
+ sgdt(&gdtr_curr);
+ gdt_curr = (gdt_entry_t *)gdtr_curr.base;
+ copy_gdt_entry(gdt64, gdt_curr, read_cs());
+ copy_gdt_entry(gdt64, gdt_curr, read_ds());
+}
+
unsigned long long get_amd_sev_c_bit_mask(void)
{
if (amd_sev_enabled()) {
diff --git a/lib/x86/amd_sev.h b/lib/x86/amd_sev.h
index b73a872..0b4ff8c 100644
--- a/lib/x86/amd_sev.h
+++ b/lib/x86/amd_sev.h
@@ -40,6 +40,7 @@ bool amd_sev_enabled(void);
efi_status_t setup_amd_sev(void);
bool amd_sev_es_enabled(void);
+void copy_uefi_segments(void);
unsigned long long get_amd_sev_c_bit_mask(void);
unsigned long long get_amd_sev_addr_upperbound(void);
diff --git a/lib/x86/setup.c b/lib/x86/setup.c
index bdda337..c6eb3e9 100644
--- a/lib/x86/setup.c
+++ b/lib/x86/setup.c
@@ -324,6 +324,10 @@ static void setup_gdt_tss(void)
tss_hi->limit_low = (u16)((curr_tss_addr >> 32) & 0xffff);
tss_hi->base_low = (u16)((curr_tss_addr >> 48) & 0xffff);
+ if (amd_sev_es_enabled()) {
+ copy_uefi_segments();
+ }
+
load_gdt_tss(tss_offset);
}
--
2.33.0.259.gc128427fd7-goog
