On Mon, May 08, 2023 at 09:31:23PM +0000, Michael Brown wrote: > At TPL_HIGH_LEVEL, CPU interrupts are disabled (as per the UEFI > specification) and so we should never encounter a situation in which > an interrupt occurs at TPL_HIGH_LEVEL. The specification also > restricts usage of TPL_HIGH_LEVEL to the firmware itself. > > However, nothing prevents a rogue UEFI application from illegally > calling gBS->RaiseTPL(TPL_HIGH_LEVEL) and then deliberately violating > the invariant by enabling interrupts via the STI or equivalent > instruction. Some versions of the Microsoft Windows bootloader are > known to do this. > > NestedInterruptTplLib maintains the invariant that interrupts are > disabled at TPL_HIGH_LEVEL (even when performing the dark art of > deliberately manipulating the stack so that IRET will return with > interrupts still disabled), but does not itself rely on external code > maintaining this invariant. > > Relax the assertion that the interrupted TPL is below TPL_HIGH_LEVEL > to an error message, to allow rogue UEFI applications such as the > Microsoft Windows bootloader to continue to function. > > Ref: https://bugzilla.redhat.com/show_bug.cgi?id=2189136 > Cc: Laszlo Ersek <ler...@redhat.com> > Cc: Gerd Hoffmann <kra...@redhat.com> > Cc: Oliver Steffen <ostef...@redhat.com> > Cc: Pawel Polawski <ppola...@redhat.com> > Cc: Jiewen Yao <jiewen....@intel.com> > Cc: Ard Biesheuvel <ardb+tianoc...@kernel.org> > Cc: Jordan Justen <jordan.l.jus...@intel.com> > > Michael Brown (2): > OvmfPkg: Clarify invariants for NestedInterruptTplLib > OvmfPkg: Relax assertion that interrupts do not occur at > TPL_HIGH_LEVEL
Reviewed-by: Gerd Hoffmann <kra...@redhat.com> take care, Gerd -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#104336): https://edk2.groups.io/g/devel/message/104336 Mute This Topic: https://groups.io/mt/98771393/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
