On Thu, Mar 17, 2022 at 3:12 PM Vit Kabele <vit@xxxxxxxxx> wrote: > > If the memory at 0x40e is uninitialized, the retrieved physical_memory > address of EBDA may be beyond the low memory (i.e. above 640K). > > If so, the kernel may unintentionally access the VGA memory, that > might not be decoded or even present in case of virtualization. > > Signed-off-by: Vit Kabele <vit@xxxxxxxxx> > Reviewed-by: Rudolf Marek <r.marek@xxxxxxxxxxxx> > --- > drivers/acpi/acpica/tbxfroot.c | 7 +++++-- Changes in the ACPICA code need to be submitted to the upstream ACPICA project via https://github.com/acpica/acpica and they are pulled from there into the kernel. Of course, this applies to the next patch in the series too. > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/drivers/acpi/acpica/tbxfroot.c b/drivers/acpi/acpica/tbxfroot.c > index 9fec3df6c3ba..67b7df1c0520 100644 > --- a/drivers/acpi/acpica/tbxfroot.c > +++ b/drivers/acpi/acpica/tbxfroot.c > @@ -138,8 +138,11 @@ acpi_find_root_pointer(acpi_physical_address *table_address) > acpi_os_unmap_memory(table_ptr, ACPI_EBDA_PTR_LENGTH); > > /* EBDA present? */ > - > - if (physical_address > 0x400) { > + /* Check that the EBDA pointer from 0x40e is sane and does not point > + * above valid low memory > + */ > + if (physical_address > 0x400 && > + physical_address < 0xA0000) { > /* > * 1b) Search EBDA paragraphs (EBDA is required to be a > * minimum of 1K length) > -- > 2.30.2 >
