Hi Pierre,
Thank you for this patch.
I think we should treat algorithms that have a zero GUID as unsafe. I
have made some suggestions on those lines marked inline as [SAMI].
Regards,
Sami Mujawar
On 09/05/2023 08:40 am, pierre.gond...@arm.com wrote:
From: Pierre Gondois<pierre.gond...@arm.com>
BZ:https://bugzilla.tianocore.org/show_bug.cgi?id=4151
The EFI_RNG_PROTOCOL can rely on the RngLib. The RngLib has multiple
implementations, some of them are unsafe (e.g. BaseRngLibTimerLib).
To allow the RngDxe to detect when such implementation is used,
a GetRngGuid() function was added in a previous patch.
The EFI_RNG_PROTOCOL can advertise multiple algorithms through
Guids. The PcdCpuRngSupportedAlgorithm is currently used to
advertise the RngLib in the Arm implementation.
The issues of doing that are:
- the RngLib implementation might not use CPU instructions,
cf. the BaseRngLibTimerLib
- most platforms don't set PcdCpuRngSupportedAlgorithm
A GetRngGuid() was added to the RngLib in a previous patch,
allowing to identify the algorithm implemented by the RngLib.
Make use of this function.
Signed-off-by: Pierre Gondois<pierre.gond...@arm.com>
---
.../RngDxe/AArch64/AArch64Algo.c | 24 +++++++++----------
.../RandomNumberGenerator/RngDxe/ArmRngDxe.c | 6 ++++-
.../RandomNumberGenerator/RngDxe/RngDxe.inf | 5 ++--
3 files changed, 19 insertions(+), 16 deletions(-)
diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
b/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
index e8be217f8a8c..a1ff7bd58fda 100644
--- a/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
+++ b/SecurityPkg/RandomNumberGenerator/RngDxe/AArch64/AArch64Algo.c
@@ -10,6 +10,7 @@
#include <Library/DebugLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/ArmTrngLib.h>
+#include <Library/RngLib.h>
#include "RngDxeInternals.h"
@@ -28,9 +29,10 @@ GetAvailableAlgorithms (
VOID
)
{
- UINT64 DummyRand;
- UINT16 MajorRevision;
- UINT16 MinorRevision;
+ EFI_STATUS Status;
+ UINT16 MajorRevision;
+ UINT16 MinorRevision;
+ GUID RngGuid;
// Rng algorithms 2 times, one for the allocation, one to populate.
mAvailableAlgoArray = AllocateZeroPool (RNG_AVAILABLE_ALGO_MAX);
@@ -38,24 +40,22 @@ GetAvailableAlgorithms (
return EFI_OUT_OF_RESOURCES;
}
- // Check RngGetBytes() before advertising PcdCpuRngSupportedAlgorithm.
- if (!EFI_ERROR (RngGetBytes (sizeof (DummyRand), (UINT8 *)&DummyRand))) {
<SNIP>
+ // Identify RngLib algorithm.
+ Status = GetRngGuid (&RngGuid);
+ if (!EFI_ERROR (Status)) {
CopyMem (
&mAvailableAlgoArray[mAvailableAlgoArrayCount],
- PcdGetPtr (PcdCpuRngSupportedAlgorithm),
- sizeof (EFI_RNG_ALGORITHM)
+ RngGuid,
+ sizeof (RngGuid)
);
mAvailableAlgoArrayCount++;
- DEBUG_CODE_BEGIN ();
- if (IsZeroGuid (PcdGetPtr (PcdCpuRngSupportedAlgorithm))) {
+ if (IsZeroGuid (&RngGuid)) {
DEBUG ((
DEBUG_WARN,
- "PcdCpuRngSupportedAlgorithm should be a non-zero GUID\n"
+ "RngLib should have a non-zero GUID\n"
));
}
-
- DEBUG_CODE_END ();
}
// Raw algorithm (Trng)
...
</SNIP>
[SAMI] I think this code should do the following:
---
BOOLEAN UnSafeAlgo = FALSE;
mAvailableAlgoArrayCount = 0;
// Identify RngLib algorithm.
Status = GetRngGuid (&RngGuid);
if(!EFI_ERROR (Status)) {
if((IsZeroGuid (&RngGuid)) ||
(CompareGuid (&RngGuid, &gEfiRngAlgorithmUnSafe))) {
// Treat zero GUID as an unsafe algorithm
DEBUG ((
DEBUG_WARN,
"RngLib uses an Unsafe algorithm and "
"must not be used for production builds.\n"
));
// Set the UnSafeAlgo flag to indicate an unsafe algorithm was found
// so that it can be added at the end of the algorithm list.
UnSafeAlgo = TRUE;
} else{
CopyMem (
&mAvailableAlgoArray[mAvailableAlgoArrayCount],
&RngGuid,
sizeof(RngGuid)
);
mAvailableAlgoArrayCount++;
}
}
// Raw algorithm (Trng)
if(!EFI_ERROR (GetArmTrngVersion (&MajorRevision, &MinorRevision))) {
CopyMem (
&mAvailableAlgoArray[mAvailableAlgoArrayCount],
&gEfiRngAlgorithmRaw,
sizeof(EFI_RNG_ALGORITHM)
);
mAvailableAlgoArrayCount++;
}
// Add unsafe algorithms at the end of the list.
if(UnSafeAlgo) {
CopyMem (
&mAvailableAlgoArray[mAvailableAlgoArrayCount],
&gEfiRngAlgorithmUnSafe,
sizeof(EFI_RNG_ALGORITHM)
);
mAvailableAlgoArrayCount++;
}
---
Doing this will not need the call to RngFindDefaultAlgo () introduced in
the next patch "[PATCH v1 7/8] SecurityPkg/RngDxe: Select safe default
Rng algorithm", which can be dropped.
[SAMI]
diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c
b/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c
index ce49ff7ae661..78a18c5e1177 100644
--- a/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c
+++ b/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c
@@ -78,6 +78,7 @@ RngGetRNG (
{
EFI_STATUS Status;
UINTN Index;
+ GUID RngGuid;
if ((This == NULL) || (RNGValueLength == 0) || (RNGValue == NULL)) {
return EFI_INVALID_PARAMETER;
@@ -102,7 +103,10 @@ RngGetRNG (
}
FoundAlgo:
- if (CompareGuid (RNGAlgorithm, PcdGetPtr (PcdCpuRngSupportedAlgorithm))) {
+ Status = GetRngGuid (&RngGuid);
+ if (!EFI_ERROR (Status) &&
+ CompareGuid (RNGAlgorithm, &RngGuid))
+ {
Status = RngGetBytes (RNGValueLength, RNGValue);
return Status;
}
diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
b/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
index d6c2d30195bf..aa5743387ed9 100644
--- a/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
+++ b/SecurityPkg/RandomNumberGenerator/RngDxe/RngDxe.inf
@@ -75,13 +75,12 @@ [Guids]
gEfiRngAlgorithmX9313DesGuid ## SOMETIMES_PRODUCES ## GUID
# Unique ID of the algorithm for RNG
gEfiRngAlgorithmX931AesGuid ## SOMETIMES_PRODUCES ## GUID
# Unique ID of the algorithm for RNG
gEfiRngAlgorithmRaw ## SOMETIMES_PRODUCES ## GUID
# Unique ID of the algorithm for RNG
+ gEfiRngAlgorithmArmRndr ## SOMETIMES_PRODUCES ## GUID
# Unique ID of the algorithm for RNG
[SAMI] Can the [Guids] section be split to relect the usage across
architectures, please?
+ gEfiRngAlgorithmUnSafe ## SOMETIMES_PRODUCES ## GUID
# Unique ID of the algorithm for RNG
[Protocols]
gEfiRngProtocolGuid ## PRODUCES
-[Pcd.AARCH64]
- gEfiMdePkgTokenSpaceGuid.PcdCpuRngSupportedAlgorithm ## CONSUMES
-
[Depex]
TRUE
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