[PATCH v3 7/8] KVM: arm64: Unwind and dump nVHE HYP stacktrace
Kalesh Singh
kaleshsingh at google.com
Thu Feb 24 10:08:55 PST 2022
On Thu, Feb 24, 2022 at 4:28 AM Fuad Tabba <tabba at google.com> wrote:
>
> Hi Kalesh,
>
> On Thu, Feb 24, 2022 at 5:22 AM Kalesh Singh <kaleshsingh at google.com> wrote:
> >
> > Unwind the stack in EL1, when CONFIG_NVHE_EL2_DEBUG is enabled. This is
> > possible because CONFIG_NVHE_EL2_DEBUG disables the host stage 2 protection
> > which allows host to access the hypervisor stack pages in EL1.
>
> For this comment to be clearer, and if my understanding is correct, I
> think that it should say that CONFIG_NVHE_EL2_DEBUG allows host stage
> 2 protection to be disabled on a hyp_panic. Otherwise, on reading the
> comment one might think that CONFIG_NVHE_EL2_DEBUG runs without host
> stage 2 protection at all.
Your understanding is correct: the host stage 2 protection is only
disabled on a hyp_panic(). I'll rephrase to make it clearer.
>
> >
> > Unwinding and dumping hyp call traces is gated on CONFIG_NVHE_EL2_DEBUG
> > to avoid the potential leaking of information to the host.
> >
> > A simple stack overflow test produces the following output:
> >
> > [ 580.376051][ T412] kvm: nVHE hyp panic at: ffffffc0116145c4!
> > [ 580.378034][ T412] kvm [412]: nVHE HYP call trace:
> > [ 580.378591][ T412] kvm [412]: [<ffffffc011614934>]
> > [ 580.378993][ T412] kvm [412]: [<ffffffc01160fa48>]
> > [ 580.379386][ T412] kvm [412]: [<ffffffc0116145dc>] // Non-terminating recursive call
> > [ 580.379772][ T412] kvm [412]: [<ffffffc0116145dc>]
> > [ 580.380158][ T412] kvm [412]: [<ffffffc0116145dc>]
> > [ 580.380544][ T412] kvm [412]: [<ffffffc0116145dc>]
> > [ 580.380928][ T412] kvm [412]: [<ffffffc0116145dc>]
> > . . .
> >
> > Since nVHE hyp symbols are not included by kallsyms to avoid issues
> > with aliasing, we fallback to the vmlinux addresses. Symbolizing the
> > addresses is handled in the next patch in this series.
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
> > ---
> >
> > Changes in v3:
> > - The nvhe hyp stack unwinder now makes use of the core logic from the
> > regular kernel unwinder to avoid duplication, per Mark
> >
> > Changes in v2:
> > - Add cpu_prepare_nvhe_panic_info()
> > - Move updating the panic info to hyp_panic(), so that unwinding also
> > works for conventional nVHE Hyp-mode.
> >
> > arch/arm64/include/asm/kvm_asm.h | 19 +++
> > arch/arm64/include/asm/stacktrace.h | 12 ++
> > arch/arm64/kernel/stacktrace.c | 210 +++++++++++++++++++++++++---
> > arch/arm64/kvm/Kconfig | 5 +-
> > arch/arm64/kvm/arm.c | 2 +-
> > arch/arm64/kvm/handle_exit.c | 3 +
> > arch/arm64/kvm/hyp/nvhe/switch.c | 18 +++
> > 7 files changed, 243 insertions(+), 26 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> > index 2e277f2ed671..16efdf150a37 100644
> > --- a/arch/arm64/include/asm/kvm_asm.h
> > +++ b/arch/arm64/include/asm/kvm_asm.h
> > @@ -176,6 +176,25 @@ struct kvm_nvhe_init_params {
> > unsigned long vtcr;
> > };
> >
> > +#ifdef CONFIG_NVHE_EL2_DEBUG
> > +/*
> > + * Used by the host in EL1 to dump the nVHE hypervisor backtrace on
> > + * hyp_panic. This is possible because CONFIG_NVHE_EL2_DEBUG disables
> > + * the host stage 2 protection. See: __hyp_do_panic()
>
> Same as my comment above.
Ack
>
> > + *
> > + * @hyp_stack_base: hyp VA of the hyp_stack base.
> > + * @hyp_overflow_stack_base: hyp VA of the hyp_overflow_stack base.
> > + * @fp: hyp FP where the backtrace begins.
> > + * @pc: hyp PC where the backtrace begins.
> > + */
> > +struct kvm_nvhe_panic_info {
> > + unsigned long hyp_stack_base;
> > + unsigned long hyp_overflow_stack_base;
> > + unsigned long fp;
> > + unsigned long pc;
> > +};
> > +#endif /* CONFIG_NVHE_EL2_DEBUG */
> > +
> > /* Translate a kernel address @ptr into its equivalent linear mapping */
> > #define kvm_ksym_ref(ptr) \
> > ({ \
> > diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> > index e77cdef9ca29..18611a51cf14 100644
> > --- a/arch/arm64/include/asm/stacktrace.h
> > +++ b/arch/arm64/include/asm/stacktrace.h
> > @@ -22,6 +22,10 @@ enum stack_type {
> > STACK_TYPE_OVERFLOW,
> > STACK_TYPE_SDEI_NORMAL,
> > STACK_TYPE_SDEI_CRITICAL,
> > +#ifdef CONFIG_NVHE_EL2_DEBUG
> > + STACK_TYPE_KVM_NVHE_HYP,
> > + STACK_TYPE_KVM_NVHE_OVERFLOW,
> > +#endif /* CONFIG_NVHE_EL2_DEBUG */
> > __NR_STACK_TYPES
> > };
> >
> > @@ -147,4 +151,12 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
> > return false;
> > }
> >
> > +#ifdef CONFIG_NVHE_EL2_DEBUG
> > +void kvm_nvhe_dump_backtrace(unsigned long hyp_offset);
> > +#else
> > +static inline void kvm_nvhe_dump_backtrace(unsigned long hyp_offset)
> > +{
> > +}
> > +#endif /* CONFIG_NVHE_EL2_DEBUG */
> > +
> > #endif /* __ASM_STACKTRACE_H */
> > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> > index e4103e085681..6ec85cb69b1f 100644
> > --- a/arch/arm64/kernel/stacktrace.c
> > +++ b/arch/arm64/kernel/stacktrace.c
> > @@ -15,6 +15,8 @@
> >
> > #include <asm/irq.h>
> > #include <asm/pointer_auth.h>
> > +#include <asm/kvm_asm.h>
> > +#include <asm/kvm_hyp.h>
> > #include <asm/stack_pointer.h>
> > #include <asm/stacktrace.h>
> >
> > @@ -64,26 +66,15 @@ NOKPROBE_SYMBOL(start_backtrace);
> > * records (e.g. a cycle), determined based on the location and fp value of A
> > * and the location (but not the fp value) of B.
> > */
> > -static int notrace unwind_frame(struct task_struct *tsk,
> > - struct stackframe *frame)
> > +static int notrace __unwind_frame(struct stackframe *frame, struct stack_info *info,
> > + unsigned long (*translate_fp)(unsigned long, enum stack_type))
> > {
> > unsigned long fp = frame->fp;
> > - struct stack_info info;
> > -
> > - if (!tsk)
> > - tsk = current;
> > -
> > - /* Final frame; nothing to unwind */
> > - if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
> > - return -ENOENT;
> >
> > if (fp & 0x7)
> > return -EINVAL;
> >
> > - if (!on_accessible_stack(tsk, fp, 16, &info))
> > - return -EINVAL;
> > -
> > - if (test_bit(info.type, frame->stacks_done))
> > + if (test_bit(info->type, frame->stacks_done))
> > return -EINVAL;
> >
> > /*
> > @@ -94,28 +85,62 @@ static int notrace unwind_frame(struct task_struct *tsk,
> > *
> > * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
> > * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
> > + * KVM_NVHE_HYP -> KVM_NVHE_OVERFLOW
> > *
> > * ... but the nesting itself is strict. Once we transition from one
> > * stack to another, it's never valid to unwind back to that first
> > * stack.
> > */
> > - if (info.type == frame->prev_type) {
> > + if (info->type == frame->prev_type) {
> > if (fp <= frame->prev_fp)
> > return -EINVAL;
> > } else {
> > set_bit(frame->prev_type, frame->stacks_done);
> > }
> >
> > + /* Record fp as prev_fp before attempting to get the next fp */
> > + frame->prev_fp = fp;
> > +
> > + /*
> > + * If fp is not from the current address space perform the
> > + * necessary translation before dereferencing it to get next fp.
> > + */
> > + if (translate_fp)
> > + fp = translate_fp(fp, info->type);
> > + if (!fp)
> > + return -EINVAL;
> > +
> > /*
> > * Record this frame record's values and location. The prev_fp and
> > - * prev_type are only meaningful to the next unwind_frame() invocation.
> > + * prev_type are only meaningful to the next __unwind_frame() invocation.
> > */
> > frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
> > frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
> > - frame->prev_fp = fp;
> > - frame->prev_type = info.type;
> > -
> > frame->pc = ptrauth_strip_insn_pac(frame->pc);
> > + frame->prev_type = info->type;
> > +
> > + return 0;
> > +}
> > +
> > +static int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
> > +{
> > + unsigned long fp = frame->fp;
> > + struct stack_info info;
> > + int err;
> > +
> > + if (!tsk)
> > + tsk = current;
> > +
> > + /* Final frame; nothing to unwind */
> > + if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
> > + return -ENOENT;
> > +
> > + if (!on_accessible_stack(tsk, fp, 16, &info))
> > + return -EINVAL;
> > +
> > + err = __unwind_frame(frame, &info, NULL);
> > + if (err)
> > + return err;
> >
> > #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> > if (tsk->ret_stack &&
> > @@ -143,20 +168,27 @@ static int notrace unwind_frame(struct task_struct *tsk,
> > }
> > NOKPROBE_SYMBOL(unwind_frame);
> >
> > -static void notrace walk_stackframe(struct task_struct *tsk,
> > - struct stackframe *frame,
> > - bool (*fn)(void *, unsigned long), void *data)
> > +static void notrace __walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
> > + bool (*fn)(void *, unsigned long), void *data,
> > + int (*unwind_frame_fn)(struct task_struct *tsk, struct stackframe *frame))
> > {
> > while (1) {
> > int ret;
> >
> > if (!fn(data, frame->pc))
> > break;
> > - ret = unwind_frame(tsk, frame);
> > + ret = unwind_frame_fn(tsk, frame);
> > if (ret < 0)
> > break;
> > }
> > }
> > +
> > +static void notrace walk_stackframe(struct task_struct *tsk,
> > + struct stackframe *frame,
> > + bool (*fn)(void *, unsigned long), void *data)
> > +{
> > + __walk_stackframe(tsk, frame, fn, data, unwind_frame);
> > +}
> > NOKPROBE_SYMBOL(walk_stackframe);
> >
> > static bool dump_backtrace_entry(void *arg, unsigned long where)
> > @@ -210,3 +242,135 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
> >
> > walk_stackframe(task, &frame, consume_entry, cookie);
> > }
> > +
> > +#ifdef CONFIG_NVHE_EL2_DEBUG
> > +DECLARE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
> > +DECLARE_KVM_NVHE_PER_CPU(unsigned long [PAGE_SIZE/sizeof(long)], hyp_overflow_stack);
> > +DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_panic_info, kvm_panic_info);
> > +
> > +static inline bool kvm_nvhe_on_overflow_stack(unsigned long sp, unsigned long size,
> > + struct stack_info *info)
> > +{
> > + struct kvm_nvhe_panic_info *panic_info = this_cpu_ptr_nvhe_sym(kvm_panic_info);
> > + unsigned long low = (unsigned long)panic_info->hyp_overflow_stack_base;
> > + unsigned long high = low + PAGE_SIZE;
> > +
> > + return on_stack(sp, size, low, high, STACK_TYPE_KVM_NVHE_OVERFLOW, info);
> > +}
> > +
> > +static inline bool kvm_nvhe_on_hyp_stack(unsigned long sp, unsigned long size,
> > + struct stack_info *info)
> > +{
> > + struct kvm_nvhe_panic_info *panic_info = this_cpu_ptr_nvhe_sym(kvm_panic_info);
> > + unsigned long low = (unsigned long)panic_info->hyp_stack_base;
> > + unsigned long high = low + PAGE_SIZE;
> > +
> > + return on_stack(sp, size, low, high, STACK_TYPE_KVM_NVHE_HYP, info);
> > +}
> > +
> > +static inline bool kvm_nvhe_on_accessible_stack(unsigned long sp, unsigned long size,
> > + struct stack_info *info)
> > +{
> > + if (info)
> > + info->type = STACK_TYPE_UNKNOWN;
> > +
> > + if (kvm_nvhe_on_hyp_stack(sp, size, info))
> > + return true;
> > + if (kvm_nvhe_on_overflow_stack(sp, size, info))
> > + return true;
> > +
> > + return false;
> > +}
> > +
> > +static unsigned long kvm_nvhe_hyp_stack_kern_va(unsigned long addr)
> > +{
> > + struct kvm_nvhe_panic_info *panic_info = this_cpu_ptr_nvhe_sym(kvm_panic_info);
> > + unsigned long hyp_base, kern_base, hyp_offset;
> > +
> > + hyp_base = (unsigned long)panic_info->hyp_stack_base;
> > + hyp_offset = addr - hyp_base;
> > +
> > + kern_base = (unsigned long)*this_cpu_ptr(&kvm_arm_hyp_stack_page);
> > +
> > + return kern_base + hyp_offset;
> > +}
> > +
> > +static unsigned long kvm_nvhe_overflow_stack_kern_va(unsigned long addr)
> > +{
> > + struct kvm_nvhe_panic_info *panic_info = this_cpu_ptr_nvhe_sym(kvm_panic_info);
> > + unsigned long hyp_base, kern_base, hyp_offset;
> > +
> > + hyp_base = (unsigned long)panic_info->hyp_overflow_stack_base;
> > + hyp_offset = addr - hyp_base;
> > +
> > + kern_base = (unsigned long)this_cpu_ptr_nvhe_sym(hyp_overflow_stack);
> > +
> > + return kern_base + hyp_offset;
> > +}
> > +
> > +/*
> > + * Convert KVM nVHE hypervisor stack VA to a kernel VA.
> > + *
> > + * The nVHE hypervisor stack is mapped in the flexible 'private' VA range, to allow
> > + * for guard pages below the stack. Consequently, the fixed offset address
> > + * translation macros won't work here.
> > + *
> > + * The kernel VA is calculated as an offset from the kernel VA of the hypervisor
> > + * stack base. See: kvm_nvhe_hyp_stack_kern_va(), kvm_nvhe_overflow_stack_kern_va()
> > + */
> > +static unsigned long kvm_nvhe_stack_kern_va(unsigned long addr,
> > + enum stack_type type)
> > +{
> > + switch (type) {
> > + case STACK_TYPE_KVM_NVHE_HYP:
> > + return kvm_nvhe_hyp_stack_kern_va(addr);
> > + case STACK_TYPE_KVM_NVHE_OVERFLOW:
> > + return kvm_nvhe_overflow_stack_kern_va(addr);
> > + default:
> > + return 0UL;
> > + }
> > +}
> > +
> > +static int notrace kvm_nvhe_unwind_frame(struct task_struct *tsk,
> > + struct stackframe *frame)
> > +{
> > + struct stack_info info;
> > +
> > + if (!kvm_nvhe_on_accessible_stack(frame->fp, 16, &info))
> > + return -EINVAL;
> > +
> > + return __unwind_frame(frame, &info, kvm_nvhe_stack_kern_va);
> > +}
> > +
> > +static bool kvm_nvhe_dump_backtrace_entry(void *arg, unsigned long where)
> > +{
> > + unsigned long va_mask = GENMASK_ULL(vabits_actual - 1, 0);
> > + unsigned long hyp_offset = (unsigned long)arg;
> > +
> > + where &= va_mask; /* Mask tags */
> > + where += hyp_offset; /* Convert to kern addr */
> > +
> > + kvm_err("[<%016lx>] %pB\n", where, (void *)where);
> > +
> > + return true;
> > +}
> > +
> > +static void notrace kvm_nvhe_walk_stackframe(struct task_struct *tsk,
> > + struct stackframe *frame,
> > + bool (*fn)(void *, unsigned long), void *data)
> > +{
> > + __walk_stackframe(tsk, frame, fn, data, kvm_nvhe_unwind_frame);
> > +}
> > +
> > +void kvm_nvhe_dump_backtrace(unsigned long hyp_offset)
> > +{
> > + struct kvm_nvhe_panic_info *panic_info = this_cpu_ptr_nvhe_sym(kvm_panic_info);
> > + struct stackframe frame;
> > +
> > + start_backtrace(&frame, panic_info->fp, panic_info->pc);
> > + pr_err("nVHE HYP call trace:\n");
> > + kvm_nvhe_walk_stackframe(NULL, &frame, kvm_nvhe_dump_backtrace_entry,
> > + (void *)hyp_offset);
> > + pr_err("---- end of nVHE HYP call trace ----\n");
> > +}
> > +#endif /* CONFIG_NVHE_EL2_DEBUG */
> > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> > index 8a5fbbf084df..75f2c8255ff0 100644
> > --- a/arch/arm64/kvm/Kconfig
> > +++ b/arch/arm64/kvm/Kconfig
> > @@ -51,8 +51,9 @@ config NVHE_EL2_DEBUG
> > depends on KVM
> > help
> > Say Y here to enable the debug mode for the non-VHE KVM EL2 object.
> > - Failure reports will BUG() in the hypervisor. This is intended for
> > - local EL2 hypervisor development.
> > + Failure reports will BUG() in the hypervisor; and panics will print
> > + the hypervisor call stack. This is intended for local EL2 hypervisor
> > + development.
>
> Nit: maybe for clarity you could rephrase as "calls to hyp_panic()
> will result in printing the hypervisor call stack".
Ack. I'll update in the next version.
Thanks,
Kalesh
>
> Thanks,
> /fuad
>
>
> >
> > If unsure, say N.
> >
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index 7a23630c4a7f..66c07c04eb52 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -49,7 +49,7 @@ DEFINE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
> >
> > DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
> >
> > -static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
> > +DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
> > unsigned long kvm_arm_hyp_percpu_base[NR_CPUS];
> > DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
> >
> > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> > index e3140abd2e2e..ff69dff33700 100644
> > --- a/arch/arm64/kvm/handle_exit.c
> > +++ b/arch/arm64/kvm/handle_exit.c
> > @@ -17,6 +17,7 @@
> > #include <asm/kvm_emulate.h>
> > #include <asm/kvm_mmu.h>
> > #include <asm/debug-monitors.h>
> > +#include <asm/stacktrace.h>
> > #include <asm/traps.h>
> >
> > #include <kvm/arm_hypercalls.h>
> > @@ -326,6 +327,8 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
> > kvm_err("nVHE hyp panic at: %016llx!\n", elr_virt + hyp_offset);
> > }
> >
> > + kvm_nvhe_dump_backtrace(hyp_offset);
> > +
> > /*
> > * Hyp has panicked and we're going to handle that by panicking the
> > * kernel. The kernel offset will be revealed in the panic so we're
> > diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> > index efc20273a352..b8ecffc47424 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> > @@ -37,6 +37,22 @@ DEFINE_PER_CPU(unsigned long, kvm_hyp_vector);
> > #ifdef CONFIG_NVHE_EL2_DEBUG
> > DEFINE_PER_CPU(unsigned long [PAGE_SIZE/sizeof(long)], hyp_overflow_stack)
> > __aligned(16);
> > +DEFINE_PER_CPU(struct kvm_nvhe_panic_info, kvm_panic_info);
> > +
> > +static inline void cpu_prepare_nvhe_panic_info(void)
> > +{
> > + struct kvm_nvhe_panic_info *panic_info = this_cpu_ptr(&kvm_panic_info);
> > + struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
> > +
> > + panic_info->hyp_stack_base = (unsigned long)(params->stack_hyp_va - PAGE_SIZE);
> > + panic_info->hyp_overflow_stack_base = (unsigned long)this_cpu_ptr(hyp_overflow_stack);
> > + panic_info->fp = (unsigned long)__builtin_frame_address(0);
> > + panic_info->pc = _THIS_IP_;
> > +}
> > + #else
> > +static inline void cpu_prepare_nvhe_panic_info(void)
> > +{
> > +}
> > #endif
> >
> > static void __activate_traps(struct kvm_vcpu *vcpu)
> > @@ -360,6 +376,8 @@ asmlinkage void __noreturn hyp_panic(void)
> > struct kvm_cpu_context *host_ctxt;
> > struct kvm_vcpu *vcpu;
> >
> > + cpu_prepare_nvhe_panic_info();
> > +
> > host_ctxt = &this_cpu_ptr(&kvm_host_data)->host_ctxt;
> > vcpu = host_ctxt->__hyp_running_vcpu;
> >
> > --
> > 2.35.1.473.g83b2b277ed-goog
> >
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