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KVM: arm64: Add PKVM_DISABLE_STAGE2_ON_PANIC

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On NVHE_EL2_DEBUG, when using pKVM, the host stage-2 is relaxed to grant
the kernel access to the stacktrace, hypervisor bug table and text to
symbolize addresses. This is unsafe for production. In preparation for
adding more debug options to NVHE_EL2_DEBUG, decouple the stage-2
relaxation into a separate option.

While at it, rename PROTECTED_NVHE_STACKTRACE into PKVM_STACKTRACE,
following the same naming scheme as PKVM_DISABLE_STAGE2_ON_PANIC.

Reviewed-by: Kalesh Singh <kaleshsingh@google.com>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://patch.msgid.link/20260309162516.2623589-20-vdonnefort@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Vincent Donnefort 2026-03-09 16:25:05 +00:00 committed by Marc Zyngier
parent a717943d8e
commit 9019e82c7e
5 changed files with 48 additions and 32 deletions
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62
arch/arm64/kvm/Kconfig
View File

@ -42,32 +42,10 @@ menuconfig KVM
If unsure, say N.
config NVHE_EL2_DEBUG
bool "Debug mode for non-VHE EL2 object"
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.
If unsure, say N.
config PROTECTED_NVHE_STACKTRACE
bool "Protected KVM hypervisor stacktraces"
depends on NVHE_EL2_DEBUG
default n
help
Say Y here to enable pKVM hypervisor stacktraces on hyp_panic()
If using protected nVHE mode, but cannot afford the associated
memory cost (less than 0.75 page per CPU) of pKVM stacktraces,
say N.
If unsure, or not using protected nVHE (pKVM), say N.
if KVM
config PTDUMP_STAGE2_DEBUGFS
bool "Present the stage-2 pagetables to debugfs"
depends on KVM
depends on DEBUG_KERNEL
depends on DEBUG_FS
depends on ARCH_HAS_PTDUMP
@ -82,4 +60,42 @@ config PTDUMP_STAGE2_DEBUGFS
If in doubt, say N.
config NVHE_EL2_DEBUG
bool "Debug mode for non-VHE EL2 object"
default n
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.
If unsure, say N.
if NVHE_EL2_DEBUG
config PKVM_DISABLE_STAGE2_ON_PANIC
bool "Disable the host stage-2 on panic"
default n
help
Relax the host stage-2 on hypervisor panic to allow the kernel to
unwind and symbolize the hypervisor stacktrace. This however tampers
the system security. This is intended for local EL2 hypervisor
development.
If unsure, say N.
config PKVM_STACKTRACE
bool "Protected KVM hypervisor stacktraces"
depends on PKVM_DISABLE_STAGE2_ON_PANIC
default y
help
Say Y here to enable pKVM hypervisor stacktraces on hyp_panic()
If using protected nVHE mode, but cannot afford the associated
memory cost (less than 0.75 page per CPU) of pKVM stacktraces,
say N.
If unsure, or not using protected nVHE (pKVM), say N.
endif # NVHE_EL2_DEBUG
endif # KVM
endif # VIRTUALIZATION

2
arch/arm64/kvm/handle_exit.c
View File

@ -539,7 +539,7 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
/* All hyp bugs, including warnings, are treated as fatal. */
if (!is_protected_kvm_enabled() ||
IS_ENABLED(CONFIG_NVHE_EL2_DEBUG)) {
IS_ENABLED(CONFIG_PKVM_DISABLE_STAGE2_ON_PANIC)) {
struct bug_entry *bug = find_bug(elr_in_kimg);
if (bug)

2
arch/arm64/kvm/hyp/nvhe/host.S
View File

@ -120,7 +120,7 @@ SYM_FUNC_START(__hyp_do_panic)
mov x29, x0
#ifdef CONFIG_NVHE_EL2_DEBUG
#ifdef PKVM_DISABLE_STAGE2_ON_PANIC
/* Ensure host stage-2 is disabled */
mrs x0, hcr_el2
bic x0, x0, #HCR_VM

6
arch/arm64/kvm/hyp/nvhe/stacktrace.c
View File

@ -34,7 +34,7 @@ static void hyp_prepare_backtrace(unsigned long fp, unsigned long pc)
stacktrace_info->pc = pc;
}
#ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
#ifdef CONFIG_PKVM_STACKTRACE
#include <asm/stacktrace/nvhe.h>
DEFINE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)], pkvm_stacktrace);
@ -134,11 +134,11 @@ static void pkvm_save_backtrace(unsigned long fp, unsigned long pc)
unwind(&state, pkvm_save_backtrace_entry, &idx);
}
#else /* !CONFIG_PROTECTED_NVHE_STACKTRACE */
#else /* !CONFIG_PKVM_STACKTRACE */
static void pkvm_save_backtrace(unsigned long fp, unsigned long pc)
{
}
#endif /* CONFIG_PROTECTED_NVHE_STACKTRACE */
#endif /* CONFIG_PKVM_STACKTRACE */
/*
* kvm_nvhe_prepare_backtrace - prepare to dump the nVHE backtrace

8
arch/arm64/kvm/stacktrace.c
View File

@ -197,7 +197,7 @@ static void hyp_dump_backtrace(unsigned long hyp_offset)
kvm_nvhe_dump_backtrace_end();
}
#ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
#ifdef CONFIG_PKVM_STACKTRACE
DECLARE_KVM_NVHE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)],
pkvm_stacktrace);
@ -225,12 +225,12 @@ static void pkvm_dump_backtrace(unsigned long hyp_offset)
kvm_nvhe_dump_backtrace_entry((void *)hyp_offset, stacktrace[i]);
kvm_nvhe_dump_backtrace_end();
}
#else /* !CONFIG_PROTECTED_NVHE_STACKTRACE */
#else /* !CONFIG_PKVM_STACKTRACE */
static void pkvm_dump_backtrace(unsigned long hyp_offset)
{
kvm_err("Cannot dump pKVM nVHE stacktrace: !CONFIG_PROTECTED_NVHE_STACKTRACE\n");
kvm_err("Cannot dump pKVM nVHE stacktrace: !CONFIG_PKVM_STACKTRACE\n");
}
#endif /* CONFIG_PROTECTED_NVHE_STACKTRACE */
#endif /* CONFIG_PKVM_STACKTRACE */
/*
* kvm_nvhe_dump_backtrace - Dump KVM nVHE hypervisor backtrace.