Hi Marc,
On 19/04/2024 11:29, Marc Zyngier wrote:
FEAT_NV has the interesting property of relying on ERET being
trapped. An added complexity is that it also traps ERETAA and
ERETAB, meaning that the Pointer Authentication aspect of these
instruction must be emulated.
Add an emulation of Pointer Authentication, limited to ERETAx
(always using SP_EL2 as the modifier and ELR_EL2 as the pointer),
using the Generic Authentication instructions.
The emulation, however small, is placed in its own compilation
unit so that it can be avoided if the configuration doesn't
include it (or the toolchan in not up to the task).
Reviewed-by: Joey Gouly <joey.gouly@xxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_nested.h | 12 ++
arch/arm64/include/asm/pgtable-hwdef.h | 1 +
arch/arm64/kvm/Makefile | 1 +
arch/arm64/kvm/pauth.c | 196 +++++++++++++++++++++++++
4 files changed, 210 insertions(+)
create mode 100644 arch/arm64/kvm/pauth.c
diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
index dbc4e3a67356..5e0ab0596246 100644
--- a/arch/arm64/include/asm/kvm_nested.h
+++ b/arch/arm64/include/asm/kvm_nested.h
@@ -64,4 +64,16 @@ extern bool forward_smc_trap(struct kvm_vcpu *vcpu);
int kvm_init_nv_sysregs(struct kvm *kvm);
+#ifdef CONFIG_ARM64_PTR_AUTH
+bool kvm_auth_eretax(struct kvm_vcpu *vcpu, u64 *elr);
+#else
+static inline bool kvm_auth_eretax(struct kvm_vcpu *vcpu, u64 *elr)
+{
+ /* We really should never execute this... */
+ WARN_ON_ONCE(1);
+ *elr = 0xbad9acc0debadbad;
+ return false;
+}
+#endif
+
#endif /* __ARM64_KVM_NESTED_H */
diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index ef207a0d4f0d..9943ff0af4c9 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -297,6 +297,7 @@
#define TCR_TBI1 (UL(1) << 38)
#define TCR_HA (UL(1) << 39)
#define TCR_HD (UL(1) << 40)
+#define TCR_TBID0 (UL(1) << 51)
#define TCR_TBID1 (UL(1) << 52)
#define TCR_NFD0 (UL(1) << 53)
#define TCR_NFD1 (UL(1) << 54)
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index c0c050e53157..04882b577575 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -23,6 +23,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
vgic/vgic-its.o vgic/vgic-debug.o
kvm-$(CONFIG_HW_PERF_EVENTS) += pmu-emul.o pmu.o
+kvm-$(CONFIG_ARM64_PTR_AUTH) += pauth.o
always-y := hyp_constants.h hyp-constants.s
diff --git a/arch/arm64/kvm/pauth.c b/arch/arm64/kvm/pauth.c
new file mode 100644
index 000000000000..a3a5c404375b
--- /dev/null
+++ b/arch/arm64/kvm/pauth.c
@@ -0,0 +1,196 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 - Google LLC
+ * Author: Marc Zyngier <maz@xxxxxxxxxx>
+ *
+ * Primitive PAuth emulation for ERETAA/ERETAB.
+ *
+ * This code assumes that is is run from EL2, and that it is part of
+ * the emulation of ERETAx for a guest hypervisor. That's a lot of
+ * baked-in assumptions and shortcuts.
+ *
+ * Do no reuse for anything else!
+ */
+
+#include <linux/kvm_host.h>
+
+#include <asm/kvm_emulate.h>
+#include <asm/pointer_auth.h>
+
+static u64 compute_pac(struct kvm_vcpu *vcpu, u64 ptr,
+ struct ptrauth_key ikey)
+{
+ struct ptrauth_key gkey;
+ u64 mod, pac = 0;
+
+ preempt_disable();
+
+ if (!vcpu_get_flag(vcpu, SYSREGS_ON_CPU))
+ mod = __vcpu_sys_reg(vcpu, SP_EL2);
+ else
+ mod = read_sysreg(sp_el1);
+
+ gkey.lo = read_sysreg_s(SYS_APGAKEYLO_EL1);
+ gkey.hi = read_sysreg_s(SYS_APGAKEYHI_EL1);
+
+ __ptrauth_key_install_nosync(APGA, ikey);
+ isb();
+
+ asm volatile(ARM64_ASM_PREAMBLE ".arch_extension pauth\n"
+ "pacga %0, %1, %2" : "=r" (pac) : "r" (ptr), "r" (mod));
+ isb();
Some of our builders currently have an older version of GCC (v6) and
after this change I am seeing ...
CC arch/arm64/kvm/pauth.o
/tmp/ccohst0v.s: Assembler messages:
/tmp/ccohst0v.s:1177: Error: unknown architectural extension `pauth'
/tmp/ccohst0v.s:1177: Error: unknown mnemonic `pacga' -- `pacga x21,x22,x0'
/local/workdir/tegra/mlt-linux_next/kernel/scripts/Makefile.build:244: recipe for target 'arch/arm64/kvm/pauth.o' failed
make[5]: *** [arch/arm64/kvm/pauth.o] Error 1
/local/workdir/tegra/mlt-linux_next/kernel/scripts/Makefile.build:485: recipe for target 'arch/arm64/kvm' failed
make[4]: *** [arch/arm64/kvm] Error 2
/local/workdir/tegra/mlt-linux_next/kernel/scripts/Makefile.build:485: recipe for target 'arch/arm64' failed
make[3]: *** [arch/arm64] Error 2
I know this is pretty old now and I am trying to get these builders
updated. However, the kernel docs still show that GCC v5.1 is
supported [0].
Jon
[0] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/process/changes.rst
--
nvpublic
