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[USETUP]: Improve the bootsector validity check performed in IsThereAValidBootSector:

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- Check for the first 3 bytes (and not 4) of the bootsector to not be zero (that's our criterium for a "valid instruction"). Therefore, a bootsector starting with "00 00 00 xx" (with xx the first byte of a volume identifier) is detected as invalid (because the BIOS won't be able to run it anyways) and therefore, needs to be overwritten.
- Check that its last 2 bytes are the valid 0xAA55 signature.
These improvements were suggested by Serge Gautherie and Peter Hater.
CORE-4870 CORE-12672 CORE-13188
- Move a DPRINT1 around.

svn path=/trunk/; revision=74512
This commit is contained in:
Hermès Bélusca-Maïto 2017-05-09 15:31:53 +00:00
parent 16e06b89aa
commit f06734e55d
2 changed files with 22 additions and 18 deletions
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35
reactos/base/setup/usetup/bootsup.c
View file

@ -630,12 +630,14 @@ BOOLEAN
IsThereAValidBootSector(PWSTR RootPath)
{
/*
* Check the first DWORD (4 bytes) of the bootsector for a potential
* "valid" instruction (the BIOS starts execution of the bootsector
* at its beginning). Currently the criterium is that this DWORD must
* be non-zero.
* We first demand that the bootsector has a valid signature at its end.
* We then check the first 3 bytes (as a ULONG) of the bootsector for a
* potential "valid" instruction (the BIOS starts execution of the bootsector
* at its beginning). Currently this criterium is that this ULONG must be
* non-zero. If both these tests pass, then the bootsector is valid; otherwise
* it is invalid and certainly needs to be overwritten.
*/
BOOLEAN IsValid = FALSE;
NTSTATUS Status;
UNICODE_STRING Name;
OBJECT_ATTRIBUTES ObjectAttributes;
@ -666,10 +668,9 @@ IsThereAValidBootSector(PWSTR RootPath)
0,
FILE_SYNCHRONOUS_IO_NONALERT);
if (!NT_SUCCESS(Status))
{
RtlFreeHeap(ProcessHeap, 0, BootSector);
return FALSE; // Status;
}
goto Quit;
RtlZeroMemory(BootSector, SECTORSIZE);
FileOffset.QuadPart = 0ULL;
Status = NtReadFile(FileHandle,
@ -682,16 +683,20 @@ IsThereAValidBootSector(PWSTR RootPath)
&FileOffset,
NULL);
NtClose(FileHandle);
if (!NT_SUCCESS(Status))
goto Quit;
Instruction = *(PULONG)BootSector;
/* Check the instruction; we use a ULONG to read three bytes */
Instruction = (*(PULONG)BootSector) & 0x00FFFFFF;
IsValid = (Instruction != 0x00000000);
/* Check the bootsector signature */
IsValid &= (*(PUSHORT)(BootSector + 0x1fe) == 0xaa55);
Quit:
/* Free the boot sector */
RtlFreeHeap(ProcessHeap, 0, BootSector);
if (!NT_SUCCESS(Status))
return FALSE; // Status;
return (Instruction != 0x00000000);
return IsValid; // Status;
}
NTSTATUS

5
reactos/base/setup/usetup/interface/usetup.c
View file

@ -4442,9 +4442,6 @@ BootLoaderHarddiskMbrPage(PINPUT_RECORD Ir)
wcscpy(SourceMbrPathBuffer, SourceRootPath.Buffer);
wcscat(SourceMbrPathBuffer, L"\\loader\\dosmbr.bin");
DPRINT1("Install MBR bootcode: %S ==> %S\n",
SourceMbrPathBuffer, DestinationDevicePathBuffer);
if (IsThereAValidBootSector(DestinationDevicePathBuffer))
{
/* Save current MBR */
@ -4460,6 +4457,8 @@ BootLoaderHarddiskMbrPage(PINPUT_RECORD Ir)
}
}
DPRINT1("Install MBR bootcode: %S ==> %S\n",
SourceMbrPathBuffer, DestinationDevicePathBuffer);
Status = InstallMbrBootCodeToDisk(SourceMbrPathBuffer,
DestinationDevicePathBuffer);
if (!NT_SUCCESS(Status))