We currently save/restore sp_el0 in C code. This is a bit unsafe,
as a lot of the C code expects 'current' to be accessible from
there (and the opportunity to run kernel code in HYP is specially
great with VHE).
Instead, let's move the save/restore of sp_el0 to the assembly
code (in __guest_enter), making sure that sp_el0 is correct
very early on when we exit the guest, and is preserved as long
as possible to its host value when we enter the guest.
Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
arch/arm64/kvm/hyp/entry.S | 23 +++++++++++++++++++++++
arch/arm64/kvm/hyp/sysreg-sr.c | 17 +++--------------
2 files changed, 26 insertions(+), 14 deletions(-)
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index d22d0534dd60..90186cf6473e 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -18,6 +18,7 @@
#define CPU_GP_REG_OFFSET(x) (CPU_GP_REGS + x)
#define CPU_XREG_OFFSET(x) CPU_GP_REG_OFFSET(CPU_USER_PT_REGS + 8*x)
+#define CPU_SP_EL0_OFFSET (CPU_XREG_OFFSET(30) + 8)
.text
.pushsection .hyp.text, "ax"
@@ -47,6 +48,16 @@
ldp x29, lr, [\ctxt, #CPU_XREG_OFFSET(29)]
.endm
+.macro save_sp_el0 ctxt, tmp
+ mrs \tmp, sp_el0
+ str \tmp, [\ctxt, #CPU_SP_EL0_OFFSET]
+.endm
+
+.macro restore_sp_el0 ctxt, tmp
+ ldr \tmp, [\ctxt, #CPU_SP_EL0_OFFSET]
+ msr sp_el0, \tmp
+.endm
+
/*
* u64 __guest_enter(struct kvm_vcpu *vcpu,
* struct kvm_cpu_context *host_ctxt);
@@ -60,6 +71,9 @@ SYM_FUNC_START(__guest_enter)
// Store the host regs
save_callee_saved_regs x1
+ // Save the host's sp_el0
+ save_sp_el0 x1, x2
+
// Now the host state is stored if we have a pending RAS SError it must
// affect the host. If any asynchronous exception is pending we defer
// the guest entry. The DSB isn't necessary before v8.2 as any SError
@@ -83,6 +97,9 @@ alternative_else_nop_endif
// when this feature is enabled for kernel code.
ptrauth_switch_to_guest x29, x0, x1, x2
+ // Restore the guest's sp_el0
+ restore_sp_el0 x29, x0
+
// Restore guest regs x0-x17
ldp x0, x1, [x29, #CPU_XREG_OFFSET(0)]
ldp x2, x3, [x29, #CPU_XREG_OFFSET(2)]
@@ -130,6 +147,9 @@ SYM_INNER_LABEL(__guest_exit, SYM_L_GLOBAL)
// Store the guest regs x18-x29, lr
save_callee_saved_regs x1
+ // Store the guest's sp_el0
+ save_sp_el0 x1, x2
+
get_host_ctxt x2, x3
// Macro ptrauth_switch_to_guest format:
@@ -139,6 +159,9 @@ SYM_INNER_LABEL(__guest_exit, SYM_L_GLOBAL)
// when this feature is enabled for kernel code.
ptrauth_switch_to_host x1, x2, x3, x4, x5
+ // Restore the hosts's sp_el0
+ restore_sp_el0 x2, x3
+
// Now restore the host regs
restore_callee_saved_regs x2
diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index 75b1925763f1..6d2df9fe0b5d 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -15,8 +15,9 @@
/*
* Non-VHE: Both host and guest must save everything.
*
- * VHE: Host and guest must save mdscr_el1 and sp_el0 (and the PC and pstate,
- * which are handled as part of the el2 return state) on every switch.
+ * VHE: Host and guest must save mdscr_el1 and sp_el0 (and the PC and
+ * pstate, which are handled as part of the el2 return state) on every
+ * switch (sp_el0 is being dealt with in the assembly code).
* tpidr_el0 and tpidrro_el0 only need to be switched when going
* to host userspace or a different VCPU. EL1 registers only need to be
* switched when potentially going to run a different VCPU. The latter two
@@ -26,12 +27,6 @@
static void __hyp_text __sysreg_save_common_state(struct kvm_cpu_context *ctxt)
{
ctxt->sys_regs[MDSCR_EL1] = read_sysreg(mdscr_el1);
-
- /*
- * The host arm64 Linux uses sp_el0 to point to 'current' and it must
- * therefore be saved/restored on every entry/exit to/from the guest.
- */
- ctxt->gp_regs.regs.sp = read_sysreg(sp_el0);
}
static void __hyp_text __sysreg_save_user_state(struct kvm_cpu_context *ctxt)
@@ -99,12 +94,6 @@ NOKPROBE_SYMBOL(sysreg_save_guest_state_vhe);
static void __hyp_text __sysreg_restore_common_state(struct kvm_cpu_context *ctxt)
{
write_sysreg(ctxt->sys_regs[MDSCR_EL1], mdscr_el1);
-
- /*
- * The host arm64 Linux uses sp_el0 to point to 'current' and it must
- * therefore be saved/restored on every entry/exit to/from the guest.
- */
- write_sysreg(ctxt->gp_regs.regs.sp, sp_el0);
}
static void __hyp_text __sysreg_restore_user_state(struct kvm_cpu_context *ctxt)
--
2.26.2
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