On 13/04/2021 10:32, Michal Orzel wrote:
Hi Julien,
On 13.04.2021 11:07, Julien Grall wrote:
Hi Michal,
On 13/04/2021 09:24, Michal Orzel wrote:
ThumbEE(T32EE) was introduced in ARMv7 and removed in ARMv8.
In 2011 ARM deprecated any use of the ThumbEE instruction set.
This doesn't mean this is not present in any CPU. In fact, in the same section
(see A2.10 in ARM DDI 0406C.d):
"ThumbEE is both the name of the instruction set and the name of the extension
that provides support for that
instruction set. The ThumbEE Extension is:
- Required in implementations of the ARMv7-A profile.
- Optional in implementations of the ARMv7-R profile.
"
This feature is untested and as per my understanding
there are no reported users for it. >
Remove all the bits related to it.
Signed-off-by: Michal Orzel <michal.or...@arm.com> > ---
xen/arch/arm/cpufeature.c | 3 +++
xen/arch/arm/domain.c | 12 ------------
xen/arch/arm/setup.c | 3 +--
xen/include/asm-arm/cpregs.h | 6 ------
xen/include/asm-arm/cpufeature.h | 1 -
xen/include/asm-arm/domain.h | 1 -
6 files changed, 4 insertions(+), 22 deletions(-)
diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
index 1d88783809..82265a72f4 100644
--- a/xen/arch/arm/cpufeature.c
+++ b/xen/arch/arm/cpufeature.c
@@ -209,6 +209,9 @@ static int __init create_guest_cpuinfo(void)
guest_cpuinfo.pfr32.ras = 0;
guest_cpuinfo.pfr32.ras_frac = 0;
+ /* Hide ThumbEE support */
+ guest_cpuinfo.pfr32.thumbee = 0;
Even if you hide the feature from the guest, the registers are still
accessible. So you are not removing support but just opening a potential
security hole as the registers now gets shared...
Looking at the spec, it doesn't look like it is possible to trap them.
Looking at the spec for ARMv7A/R:
https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/System-Control-Registers-in-a-VMSA-implementation/VMSA-System-control-registers-descriptions--in-register-order/HSTR--Hyp-System-Trap-Register--Virtualization-Extensions
we can trap Thumbee operations.
This means that we will not open the security hole.
That's for pointing that out. However, I am not still not sure why you
want to drop the code. Yes this is technically untested, but:
1) The change is very small
2) There are CPU out there supporting it (it is mandated after all).
--
Julien Grall
