KVM: arm64: Forbid kprobing of the VHE world-switch code

James Morse · Marc Zyngier · commit 7d82602909ed · 2019-02-07T11:44:47.000Z
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: 3f5c90b ("KVM: arm64: Introduce VHE-specific kvm_vcpu_run") Acked-by: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
diff --git 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
@@ -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)
 {

Original file line number	Diff line number	Diff line change
`@@ -23,6 +23,7 @@`
`23`	`23`	`#include <kvm/arm_psci.h>`
`24`	`24`
`25`	`25`	`#include <asm/cpufeature.h>`
	`26`	`+#include <asm/kprobes.h>`
`26`	`27`	`#include <asm/kvm_asm.h>`
`27`	`28`	`#include <asm/kvm_emulate.h>`
`28`	`29`	`#include <asm/kvm_host.h>`
`@@ -107,6 +108,7 @@ static void activate_traps_vhe(struct kvm_vcpu *vcpu)`
`107`	`108`
`108`	`109`	`write_sysreg(kvm_get_hyp_vector(), vbar_el1);`
`109`	`110`	`}`
	`111`	`+NOKPROBE_SYMBOL(activate_traps_vhe);`
`110`	`112`
`111`	`113`	`static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)`
`112`	`114`	`{`
`@@ -154,6 +156,7 @@ static void deactivate_traps_vhe(void)`
`154`	`156`	`write_sysreg(CPACR_EL1_DEFAULT, cpacr_el1);`
`155`	`157`	`write_sysreg(vectors, vbar_el1);`
`156`	`158`	`}`
	`159`	`+NOKPROBE_SYMBOL(deactivate_traps_vhe);`
`157`	`160`
`158`	`161`	`static void __hyp_text __deactivate_traps_nvhe(void)`
`159`	`162`	`{`
`@@ -513,6 +516,7 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)`
`513`	`516`
`514`	`517`	`return exit_code;`
`515`	`518`	`}`
	`519`	`+NOKPROBE_SYMBOL(kvm_vcpu_run_vhe);`
`516`	`520`
`517`	`521`	`/* Switch to the guest for legacy non-VHE systems */`
`518`	`522`	`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,`
`620`	`624`	`read_sysreg_el2(esr), read_sysreg_el2(far),`
`621`	`625`	`read_sysreg(hpfar_el2), par, vcpu);`
`622`	`626`	`}`
	`627`	`+NOKPROBE_SYMBOL(__hyp_call_panic_vhe);`
`623`	`628`
`624`	`629`	`void __hyp_text __noreturn hyp_panic(struct kvm_cpu_context *host_ctxt)`
`625`	`630`	`{`
Original file line number	Diff line number	Diff line change
`@@ -18,6 +18,7 @@`
`18`	`18`	`#include <linux/compiler.h>`
`19`	`19`	`#include <linux/kvm_host.h>`
`20`	`20`
	`21`	`+#include <asm/kprobes.h>`
`21`	`22`	`#include <asm/kvm_asm.h>`
`22`	`23`	`#include <asm/kvm_emulate.h>`
`23`	`24`	`#include <asm/kvm_hyp.h>`
`@@ -98,12 +99,14 @@ void sysreg_save_host_state_vhe(struct kvm_cpu_context *ctxt)`
`98`	`99`	`{`
`99`	`100`	`__sysreg_save_common_state(ctxt);`
`100`	`101`	`}`
	`102`	`+NOKPROBE_SYMBOL(sysreg_save_host_state_vhe);`
`101`	`103`
`102`	`104`	`void sysreg_save_guest_state_vhe(struct kvm_cpu_context *ctxt)`
`103`	`105`	`{`
`104`	`106`	`__sysreg_save_common_state(ctxt);`
`105`	`107`	`__sysreg_save_el2_return_state(ctxt);`
`106`	`108`	`}`
	`109`	`+NOKPROBE_SYMBOL(sysreg_save_guest_state_vhe);`
`107`	`110`
`108`	`111`	`static void __hyp_text __sysreg_restore_common_state(struct kvm_cpu_context *ctxt)`
`109`	`112`	`{`
`@@ -188,12 +191,14 @@ void sysreg_restore_host_state_vhe(struct kvm_cpu_context *ctxt)`
`188`	`191`	`{`
`189`	`192`	`__sysreg_restore_common_state(ctxt);`
`190`	`193`	`}`
	`194`	`+NOKPROBE_SYMBOL(sysreg_restore_host_state_vhe);`
`191`	`195`
`192`	`196`	`void sysreg_restore_guest_state_vhe(struct kvm_cpu_context *ctxt)`
`193`	`197`	`{`
`194`	`198`	`__sysreg_restore_common_state(ctxt);`
`195`	`199`	`__sysreg_restore_el2_return_state(ctxt);`
`196`	`200`	`}`
	`201`	`+NOKPROBE_SYMBOL(sysreg_restore_guest_state_vhe);`
`197`	`202`
`198`	`203`	`void __hyp_text __sysreg32_save_state(struct kvm_vcpu *vcpu)`
`199`	`204`	`{`