[PATCH v3 7/8] KVM: arm64: Unwind and dump nVHE HYP stacktrace
Fuad Tabba
tabba at google.com
Thu Feb 24 04:28:03 PST 2022
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.
>
> 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.
> + *
> + * @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".
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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