6.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Marc Zyngier maz@kernel.org
commit 947051e361d551e0590777080ffc4926190f62f2 upstream.
When userspace writes to one of the core registers, we make sure to narrow the corresponding GPRs if PSTATE indicates an AArch32 context.
The code tries to check whether the context is EL0 or EL1 so that it narrows the correct registers. But it does so by checking the full PSTATE instead of PSTATE.M.
As a consequence, and if we are restoring an AArch32 EL0 context in a 64bit guest, and that PSTATE has *any* bit set outside of PSTATE.M, we narrow *all* registers instead of only the first 15, destroying the 64bit state.
Obviously, this is not something the guest is likely to enjoy.
Correctly masking PSTATE to only evaluate PSTATE.M fixes it.
Fixes: 90c1f934ed71 ("KVM: arm64: Get rid of the AArch32 register mapping code") Reported-by: Nina Schoetterl-Glausch nsg@linux.ibm.com Cc: stable@vger.kernel.org Reviewed-by: Nina Schoetterl-Glausch nsg@linux.ibm.com Acked-by: Oliver Upton oliver.upton@linux.dev Link: https://lore.kernel.org/r/20240524141956.1450304-2-maz@kernel.org Signed-off-by: Marc Zyngier maz@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kvm/guest.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm64/kvm/guest.c +++ b/arch/arm64/kvm/guest.c @@ -276,7 +276,7 @@ static int set_core_reg(struct kvm_vcpu if (*vcpu_cpsr(vcpu) & PSR_MODE32_BIT) { int i, nr_reg;
- switch (*vcpu_cpsr(vcpu)) { + switch (*vcpu_cpsr(vcpu) & PSR_AA32_MODE_MASK) { /* * Either we are dealing with user mode, and only the * first 15 registers (+ PC) must be narrowed to 32bit.