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OvmfPkg/QemuVideoDxe: avoid arithmetic on null pointer 

The real mode interrupt vector table, which we modify for the sake of
Windows 7, starts at address 0, which happens to be the representation of
null pointers on all edk2 architectures. A null pointer may never undergo
pointer arithmetic, and RH covscan justifiedly reports:

> Error: CPPCHECK_WARNING (CWE-682):
> edk2-89910a39dcfd/OvmfPkg/QemuVideoDxe/VbeShim.c:105:
> error[nullPointerArithmetic]: Pointer addition with NULL pointer.
> #  103|     //
> #  104|     Segment0Pages = 1;
> #  105|->   Int0x10       = (IVT_ENTRY *)(UINTN)Segment0 + 0x10;
> #  106|     Segment0AllocationStatus = gBS->AllocatePages (
> #  107|                                       AllocateAddress,

Fix this by calculating the EFI_PHYSICAL_ADDRESS of IVT entry 0x10 first,
and by casting the address to the right type second.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1710
Issue: scan-1002.txt
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
This commit is contained in:
Laszlo Ersek 2019-04-12 16:13:48 +02:00
parent 933f1990f5
commit 52d229238b
1 changed files with 1 additions and 1 deletions
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2
OvmfPkg/QemuVideoDxe/VbeShim.c
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@ -96,7 +96,7 @@ InstallVbeShim (
// The allocation request may fail, eg. if LegacyBiosDxe has already run.
//
Segment0Pages = 1;
Int0x10 = (IVT_ENTRY *)(UINTN)Segment0 + 0x10;
Int0x10 = (IVT_ENTRY *)(UINTN)(Segment0 + 0x10 * sizeof (IVT_ENTRY));
Segment0AllocationStatus = gBS->AllocatePages (
AllocateAddress,
EfiBootServicesCode,