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KVM: arm64: Reclaim faulting page from pKVM in spurious fault handler

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Host kernel accesses to pages that are inaccessible at stage-2 result in
the injection of a translation fault, which is fatal unless an exception
table fixup is registered for the faulting PC (e.g. for user access
routines). This is undesirable, since a get_user_pages() call could be
used to obtain a reference to a donated page and then a subsequent
access via a kernel mapping would lead to a panic().

Rework the spurious fault handler so that stage-2 faults injected back
into the host result in the target page being forcefully reclaimed when
no exception table fixup handler is registered.

Tested-by: Fuad Tabba <tabba@google.com>
Tested-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://patch.msgid.link/20260330144841.26181-27-will@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Will Deacon 2026-03-30 15:48:27 +01:00 committed by Marc Zyngier
parent 56080f53a6
commit 281a38ad29
3 changed files with 32 additions and 6 deletions
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9
arch/arm64/include/asm/virt.h
View File

@ -94,6 +94,15 @@ static inline bool is_pkvm_initialized(void)
static_branch_likely(&kvm_protected_mode_initialized);
}
#ifdef CONFIG_KVM
bool pkvm_force_reclaim_guest_page(phys_addr_t phys);
#else
static inline bool pkvm_force_reclaim_guest_page(phys_addr_t phys)
{
return false;
}
#endif
/* Reports the availability of HYP mode */
static inline bool is_hyp_mode_available(void)
{

12
arch/arm64/kvm/pkvm.c
View File

@ -569,3 +569,15 @@ int pkvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size,
WARN_ON_ONCE(1);
return -EINVAL;
}
/*
* Forcefully reclaim a page from the guest, zeroing its contents and
* poisoning the stage-2 pte so that pages can no longer be mapped at
* the same IPA. The page remains pinned until the guest is destroyed.
*/
bool pkvm_force_reclaim_guest_page(phys_addr_t phys)
{
int ret = kvm_call_hyp_nvhe(__pkvm_force_reclaim_guest_page, phys);
return !ret || ret == -EAGAIN;
}

17
arch/arm64/mm/fault.c
View File

@ -289,9 +289,6 @@ static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr,
if (!is_el1_data_abort(esr) || !esr_fsc_is_translation_fault(esr))
return false;
if (is_pkvm_stage2_abort(esr))
return false;
local_irq_save(flags);
asm volatile("at s1e1r, %0" :: "r" (addr));
isb();
@ -302,8 +299,14 @@ static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr,
* If we now have a valid translation, treat the translation fault as
* spurious.
*/
if (!(par & SYS_PAR_EL1_F))
if (!(par & SYS_PAR_EL1_F)) {
if (is_pkvm_stage2_abort(esr)) {
par &= SYS_PAR_EL1_PA;
return pkvm_force_reclaim_guest_page(par);
}
return true;
}
/*
* If we got a different type of fault from the AT instruction,
@ -389,9 +392,11 @@ static void __do_kernel_fault(unsigned long addr, unsigned long esr,
if (!is_el1_instruction_abort(esr) && fixup_exception(regs, esr))
return;
if (WARN_RATELIMIT(is_spurious_el1_translation_fault(addr, esr, regs),
"Ignoring spurious kernel translation fault at virtual address %016lx\n", addr))
if (is_spurious_el1_translation_fault(addr, esr, regs)) {
WARN_RATELIMIT(!is_pkvm_stage2_abort(esr),
"Ignoring spurious kernel translation fault at virtual address %016lx\n", addr);
return;
}
if (is_el1_mte_sync_tag_check_fault(esr)) {
do_tag_recovery(addr, esr, regs);