[edk2-devel] [PATCH 07/12] OvmfPkg/VmgExitLib: Check for an explicit DR7 cached value
Lendacky, Thomas
thomas.lendacky at amd.com
Tue Dec 15 20:51:06 UTC 2020
From: Tom Lendacky <thomas.lendacky at amd.com>
BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3108
Check the DR7 cached indicator against a specific value. This makes it
harder for a hypervisor to just write random data into that field in an
attempt to use an invalid DR7 value.
Cc: Jordan Justen <jordan.l.justen at intel.com>
Cc: Laszlo Ersek <lersek at redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel at arm.com>
Cc: Brijesh Singh <brijesh.singh at amd.com>
Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
---
OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
index 1671db3a01b1..5149ab2bc989 100644
--- a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
+++ b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
@@ -128,10 +128,13 @@ UINT64
//
// Per-CPU data mapping structure
+// Use UINT32 for cached indicators and compare to a specific value
+// so that the hypervisor can't indicate a value is cached by just
+// writing random data to that area.
//
typedef struct {
- BOOLEAN Dr7Cached;
- UINT64 Dr7;
+ UINT32 Dr7Cached;
+ UINT64 Dr7;
} SEV_ES_PER_CPU_DATA;
@@ -1489,7 +1492,7 @@ Dr7WriteExit (
}
SevEsData->Dr7 = *Register;
- SevEsData->Dr7Cached = TRUE;
+ SevEsData->Dr7Cached = 1;
return 0;
}
@@ -1533,7 +1536,7 @@ Dr7ReadExit (
// If there is a cached valued for DR7, return that. Otherwise return the
// DR7 standard reset value of 0x400 (no debug breakpoints set).
//
- *Register = (SevEsData->Dr7Cached) ? SevEsData->Dr7 : 0x400;
+ *Register = (SevEsData->Dr7Cached == 1) ? SevEsData->Dr7 : 0x400;
return 0;
}
--
2.28.0
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