Proxying the cpuif accesses at EL2 makes use of vcpu_data_guest_to_host
and co, which check the endianness, which call into vcpu_read_sys_reg...
which isn't mapped at EL2 (it was inlined before, and got moved OoL
with the VHE optimizations).
The result is of course a nice panic. Let's add some specialized
cruft to keep the broken platforms that require this hack alive.
But, this code used vcpu_data_guest_to_host(), which expected us to
write the value to host memory, instead we have trapped the guest's
read or write to an mmio-device, and are about to replay it using the
host's readl()/writel() which also perform swabbing based on the host
endianness. This goes wrong when both host and guest are big-endian,
as readl()/writel() will undo the guest's swabbing, causing the
big-endian value to be written to device-memory.
What needs doing?
A big-endian guest will have pre-swabbed data before storing, undo this.
If its necessary for the host, writel() will re-swab it.
For a read a big-endian guest expects to swab the data after the load.
The hosts's readl() will correct for host endianness, giving us the
device-memory's value in the register. For a big-endian guest, swab it
as if we'd only done the load.
For a little-endian guest, nothing needs doing as readl()/writel() leave
the correct device-memory value in registers.
Tested on Juno with that rarest of things: a big-endian 64K host.
Based on a patch from Marc Zyngier.
Reported-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Fixes: bf8feb39642b ("arm64: KVM: vgic-v2: Add GICV access from HYP")
CC: Marc Zyngier <marc.zyngier@xxxxxxx>
Signed-off-by: James Morse <james.morse@xxxxxxx>
---
This patch doesn't apply before 8a43a2b34b7d
("KVM: arm/arm64: Move arm64-only vgic-v2-sr.c file to arm64"), but the
backport is straightforward.
arch/arm64/kvm/hyp/vgic-v2-cpuif-proxy.c | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/kvm/hyp/vgic-v2-cpuif-proxy.c b/arch/arm64/kvm/hyp/vgic-v2-cpuif-proxy.c
index 86801b6055d6..39be799d0417 100644
--- a/arch/arm64/kvm/hyp/vgic-v2-cpuif-proxy.c
+++ b/arch/arm64/kvm/hyp/vgic-v2-cpuif-proxy.c
@@ -18,11 +18,20 @@
#include <linux/compiler.h>
#include <linux/irqchip/arm-gic.h>
#include <linux/kvm_host.h>
+#include <linux/swab.h>
#include <asm/kvm_emulate.h>
#include <asm/kvm_hyp.h>
#include <asm/kvm_mmu.h>
+static bool __hyp_text __is_be(struct kvm_vcpu *vcpu)
+{
+ if (vcpu_mode_is_32bit(vcpu))
+ return !!(read_sysreg_el2(spsr) & COMPAT_PSR_E_BIT);
+
+ return !!(read_sysreg(SCTLR_EL1) & SCTLR_ELx_EE);
+}
+
/*
* __vgic_v2_perform_cpuif_access -- perform a GICV access on behalf of the
* guest.
@@ -64,14 +73,19 @@ int __hyp_text __vgic_v2_perform_cpuif_access(struct kvm_vcpu *vcpu)
addr += fault_ipa - vgic->vgic_cpu_base;
if (kvm_vcpu_dabt_iswrite(vcpu)) {
- u32 data = vcpu_data_guest_to_host(vcpu,
- vcpu_get_reg(vcpu, rd),
- sizeof(u32));
+ u32 data = vcpu_get_reg(vcpu, rd);
+ if (__is_be(vcpu)) {
+ /* guest pre-swabbed data, undo this for writel() */
+ data = swab32(data);
+ }
writel_relaxed(data, addr);
} else {
u32 data = readl_relaxed(addr);
- vcpu_set_reg(vcpu, rd, vcpu_data_host_to_guest(vcpu, data,
- sizeof(u32)));
+ if (__is_be(vcpu)) {
+ /* guest expects swabbed data */
+ data = swab32(data);
+ }
+ vcpu_set_reg(vcpu, rd, data);
}
return 1;
--
2.16.2
