[PATCH v2 1/4] KVM: arm64: Forbid kprobing of the VHE world-switch code

[James Morse <james.morse@arm.com>]

On systems with VHE the kernel and KVM's world-switch code run at the
same exception level. Code that is only used on a VHE system does not
need to be annotated as __hyp_text as it can reside anywhere in the
kernel text.

__hyp_text was also used to prevent kprobes from patching breakpoint
instructions into this region, as this code runs at a different
exception level. While this is no longer true with VHE, KVM still
switches VBAR_EL1, meaning a kprobe's breakpoint executed in the
world-switch code will cause a hyp-panic.

echo "p:weasel sysreg_save_guest_state_vhe" > /sys/kernel/debug/tracing/kprobe_events
echo 1 > /sys/kernel/debug/tracing/events/kprobes/weasel/enable
lkvm run -k /boot/Image --console serial -p "console=ttyS0 earlycon=uart,mmio,0x3f8"

  # lkvm run -k /boot/Image -m 384 -c 3 --name guest-1474
  Info: Placing fdt at 0x8fe00000 - 0x8fffffff
  Info: virtio-mmio.devices=0x200@0x10000:36

  Info: virtio-mmio.devices=0x200@0x10200:37

  Info: virtio-mmio.devices=0x200@0x10400:38

[  614.178186] Kernel panic - not syncing: HYP panic:
[  614.178186] PS:404003c9 PC:ffff0000100d70e0 ESR:f2000004
[  614.178186] FAR:0000000080080000 HPFAR:0000000000800800 PAR:1d00007edbadc0de
[  614.178186] VCPU:00000000f8de32f1
[  614.178383] CPU: 2 PID: 1482 Comm: kvm-vcpu-0 Not tainted 5.0.0-rc2 #10799
[  614.178446] Call trace:
[  614.178480]  dump_backtrace+0x0/0x148
[  614.178567]  show_stack+0x24/0x30
[  614.178658]  dump_stack+0x90/0xb4
[  614.178710]  panic+0x13c/0x2d8
[  614.178793]  hyp_panic+0xac/0xd8
[  614.178880]  kvm_vcpu_run_vhe+0x9c/0xe0
[  614.178958]  kvm_arch_vcpu_ioctl_run+0x454/0x798
[  614.179038]  kvm_vcpu_ioctl+0x360/0x898
[  614.179087]  do_vfs_ioctl+0xc4/0x858
[  614.179174]  ksys_ioctl+0x84/0xb8
[  614.179261]  __arm64_sys_ioctl+0x28/0x38
[  614.179348]  el0_svc_common+0x94/0x108
[  614.179401]  el0_svc_handler+0x38/0x78
[  614.179487]  el0_svc+0x8/0xc
[  614.179558] SMP: stopping secondary CPUs
[  614.179661] Kernel Offset: disabled
[  614.179695] CPU features: 0x003,2a80aa38
[  614.179758] Memory Limit: none
[  614.179858] ---[ end Kernel panic - not syncing: HYP panic:
[  614.179858] PS:404003c9 PC:ffff0000100d70e0 ESR:f2000004
[  614.179858] FAR:0000000080080000 HPFAR:0000000000800800 PAR:1d00007edbadc0de
[  614.179858] VCPU:00000000f8de32f1 ]---

Annotate the VHE world-switch functions that aren't marked
__hyp_text using NOKPROBE_SYMBOL().

Signed-off-by: James Morse <james.morse@arm.com>
Fixes: 3f5c90b890ac ("KVM: arm64: Introduce VHE-specific kvm_vcpu_run")
---

This has been an issue since the VHE/non-VHE world-switch paths were
split.


Changes since v1:
 * Switched to NOKPROBE_SYMBOL() as this doesn't move code between
   sections.

---
 arch/arm64/kvm/hyp/switch.c    | 5 +++++
 arch/arm64/kvm/hyp/sysreg-sr.c | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index b0b1478094b4..421ebf6f7086 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -23,6 +23,7 @@
 #include <kvm/arm_psci.h>
 
 #include <asm/cpufeature.h>
+#include <asm/kprobes.h>
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_host.h>
@@ -107,6 +108,7 @@ static void activate_traps_vhe(struct kvm_vcpu *vcpu)
 
 	write_sysreg(kvm_get_hyp_vector(), vbar_el1);
 }
+NOKPROBE_SYMBOL(activate_traps_vhe);
 
 static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)
 {
@@ -154,6 +156,7 @@ static void deactivate_traps_vhe(void)
 	write_sysreg(CPACR_EL1_DEFAULT, cpacr_el1);
 	write_sysreg(vectors, vbar_el1);
 }
+NOKPROBE_SYMBOL(deactivate_traps_vhe);
 
 static void __hyp_text __deactivate_traps_nvhe(void)
 {
@@ -513,6 +516,7 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
 
 	return exit_code;
 }
+NOKPROBE_SYMBOL(kvm_vcpu_run_vhe);
 
 /* Switch to the guest for legacy non-VHE systems */
 int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
@@ -620,6 +624,7 @@ static void __hyp_call_panic_vhe(u64 spsr, u64 elr, u64 par,
 	      read_sysreg_el2(esr),   read_sysreg_el2(far),
 	      read_sysreg(hpfar_el2), par, vcpu);
 }
+NOKPROBE_SYMBOL(__hyp_call_panic_vhe);
 
 void __hyp_text __noreturn hyp_panic(struct kvm_cpu_context *host_ctxt)
 {
diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index 68d6f7c3b237..b426e2cf973c 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -18,6 +18,7 @@
 #include <linux/compiler.h>
 #include <linux/kvm_host.h>
 
+#include <asm/kprobes.h>
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_hyp.h>
@@ -98,12 +99,14 @@ void sysreg_save_host_state_vhe(struct kvm_cpu_context *ctxt)
 {
 	__sysreg_save_common_state(ctxt);
 }
+NOKPROBE_SYMBOL(sysreg_save_host_state_vhe);
 
 void sysreg_save_guest_state_vhe(struct kvm_cpu_context *ctxt)
 {
 	__sysreg_save_common_state(ctxt);
 	__sysreg_save_el2_return_state(ctxt);
 }
+NOKPROBE_SYMBOL(sysreg_save_guest_state_vhe);
 
 static void __hyp_text __sysreg_restore_common_state(struct kvm_cpu_context *ctxt)
 {
@@ -188,12 +191,14 @@ void sysreg_restore_host_state_vhe(struct kvm_cpu_context *ctxt)
 {
 	__sysreg_restore_common_state(ctxt);
 }
+NOKPROBE_SYMBOL(sysreg_restore_host_state_vhe);
 
 void sysreg_restore_guest_state_vhe(struct kvm_cpu_context *ctxt)
 {
 	__sysreg_restore_common_state(ctxt);
 	__sysreg_restore_el2_return_state(ctxt);
 }
+NOKPROBE_SYMBOL(sysreg_restore_guest_state_vhe);
 
 void __hyp_text __sysreg32_save_state(struct kvm_vcpu *vcpu)
 {
-- 
2.20.1


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