On 04/15/19 19:31, Philippe Mathieu-Daudé wrote:
> On 4/13/19 1:31 AM, Laszlo Ersek wrote:
>> RH covscan reports the following "nullptr deref" warning:
>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:312:5:
>>> warning: Dereference of null pointer
>>> # InstanceZero->NumInstancesUnion.NumInstances++;
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:509:7:
>>> note: Assuming 'OutCapList' is not equal to NULL
>>> # if (OutCapList == NULL) {
>>> # ^~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:509:3:
>>> note: Taking false branch
>>> # if (OutCapList == NULL) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:518:7:
>>> note: Assuming the condition is false
>>> # if (OutCapList->Capabilities == NULL) {
>>> # ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:518:3:
>>> note: Taking false branch
>>> # if (OutCapList->Capabilities == NULL) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:529:7:
>>> note: Assuming 'CapHdrOffsets' is not equal to NULL
>>> # if (CapHdrOffsets == NULL) {
>>> # ^~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:529:3:
>>> note: Taking false branch
>>> # if (CapHdrOffsets == NULL) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:546:3:
>>> note: Taking false branch
>>> # if (RETURN_ERROR (Status)) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:549:7:
>>> note: Assuming the condition is true
>>> # if ((PciStatusReg & EFI_PCI_STATUS_CAPABILITY) != 0) {
>>> # ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:549:3:
>>> note: Taking true branch
>>> # if ((PciStatusReg & EFI_PCI_STATUS_CAPABILITY) != 0) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:557:5:
>>> note: Taking false branch
>>> # if (RETURN_ERROR (Status)) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:565:12:
>>> note: Assuming 'NormalCapHdrOffset' is > 0
>>> # while (NormalCapHdrOffset > 0) {
>>> # ^~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:565:5:
>>> note: Loop condition is true. Entering loop body
>>> # while (NormalCapHdrOffset > 0) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:570:7:
>>> note: Taking false branch
>>> # if (RETURN_ERROR (Status)) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:574:16:
>>> note: Calling 'InsertPciCap'
>>> # Status = InsertPciCap (OutCapList, CapHdrOffsets, PciCapNormal,
>>> # ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:235:3:
>>> note: Null pointer value stored to 'InstanceZero'
>>> # InstanceZero = NULL;
>>> # ^~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:243:7:
>>> note: Assuming 'PciCap' is not equal to NULL
>>> # if (PciCap == NULL) {
>>> # ^~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:243:3:
>>> note: Taking false branch
>>> # if (PciCap == NULL) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:259:3:
>>> note: Taking false branch
>>> # if (RETURN_ERROR (Status)) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:297:3:
>>> note: Taking false branch
>>> # if (RETURN_ERROR (Status)) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:311:7:
>>> note: Assuming the condition is true
>>> # if (PciCap->Key.Instance > 0) {
>>> # ^~~~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:311:3:
>>> note: Taking true branch
>>> # if (PciCap->Key.Instance > 0) {
>>> # ^
>>> edk2-89910a39dcfd/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c:312:5:
>>> note: Dereference of null pointer
>>> # InstanceZero->NumInstancesUnion.NumInstances++;
>>> # ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> # 310| //
>>> # 311| if (PciCap->Key.Instance > 0) {
>>> # 312|-> InstanceZero->NumInstancesUnion.NumInstances++;
>>> # 313| }
>>> # 314| return RETURN_SUCCESS;
>>
>> The warning is invalid: the flagged dereferencing of "InstanceZero" is
>> gated by a condition that is only satisfied if we dereference
>> "InstanceZero" *first*.
>>
>> (Perhaps the analyzer assumes that the OrderedCollectionInsert() call,
>> just before line 259, can change the value of "PciCap->Key.Instance" via
>> the last argument:
>>
>> 254 //
>> 255 // Add PciCap to CapList.
>> 256 //
>> 257 Status = OrderedCollectionInsert (CapList->Capabilities,
>> &PciCapEntry,
>> 258 PciCap);
>> 259 if (RETURN_ERROR (Status)) {
>>
>> That assumption is incorrect.)
>>
>> Add a comment and an ASSERT().
>>
>> Cc: Ard Biesheuvel <ard.biesheu...@linaro.org>
>> Cc: Jordan Justen <jordan.l.jus...@intel.com>
>> Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1710
>> Issue: scan-0994.txt
>> Signed-off-by: Laszlo Ersek <ler...@redhat.com>
>> ---
>> OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c
>> b/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c
>> index 4968d2b478db..c6f2c726509f 100644
>> --- a/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c
>> +++ b/OvmfPkg/Library/BasePciCapLib/BasePciCapLib.c
>> @@ -298,16 +298,23 @@ InsertPciCap (
>> goto DeletePciCapFromCapList;
>> }
>>
>> //
>> // Now we can bump the instance count maintained in Instance#0, if PciCap
>> is
>> // not the first instance of (Domain, CapId).
>> //
>> if (PciCap->Key.Instance > 0) {
>> + //
>> + // Suppress invalid "nullptr dereference" compiler/analyzer warnings:
>> the
>> + // only way for "PciCap->Key.Instance" to be positive here is for it to
>> + // have been assigned *from* dereferencing "InstanceZero" above.
>> + //
>> + ASSERT (InstanceZero != NULL);
>
> What about adding a STATIC_ANALYZER_HINT() only defined by covscan?
>
> STATIC_ANALYZER_HINT (InstanceZero != NULL);
We'd have to #define STATIC_ANALYZER_HINT in "MdePkg/Include/Base.h",
somehow.
>
> Regardless:
> Reviewed-by: Philippe Mathieu-Daude <phi...@redhat.com>
Thanks! (For the other reviews too.)
Laszlo
>
>> +
>> InstanceZero->NumInstancesUnion.NumInstances++;
>> }
>> return RETURN_SUCCESS;
>>
>> DeletePciCapFromCapList:
>> OrderedCollectionDelete (CapList->Capabilities, PciCapEntry, NULL);
>>
>> FreePciCap:
>>
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