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KVM: arm64: Fix clobbered ELR in sync abort/SError

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When the hypervisor receives a SError or synchronous exception (EL2h)
while running with the __kvm_hyp_vector and if ELR_EL2 doesn't point to
an extable entry, it panics indirectly by overwriting ELR with the
address of a panic handler in order for the asm routine it returns to to
ERET into the handler.

However, this clobbers ELR_EL2 for the handler itself. As a result,
hyp_panic(), when retrieving what it believes to be the PC where the
exception happened, actually ends up reading the address of the panic
handler that called it! This results in an erroneous and confusing panic
message where the source of any synchronous exception (e.g. BUG() or
kCFI) appears to be __guest_exit_panic, making it hard to locate the
actual BRK instruction.

Therefore, store the original ELR_EL2 in the per-CPU kvm_hyp_ctxt and
point the sysreg to a routine that first restores it to its previous
value before running __guest_exit_panic.

Fixes: 7db2153047 ("KVM: arm64: Restore hyp when panicking in guest context")
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20240610063244.2828978-2-ptosi@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Pierre-Clément Tosi 2024-06-10 07:32:30 +01:00 committed by Oliver Upton
parent 83a7eefedc
commit a8f0655887
3 changed files with 12 additions and 2 deletions
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1
arch/arm64/kernel/asm-offsets.c
View File

@ -128,6 +128,7 @@ int main(void)
DEFINE(VCPU_FAULT_DISR, offsetof(struct kvm_vcpu, arch.fault.disr_el1));
DEFINE(VCPU_HCR_EL2, offsetof(struct kvm_vcpu, arch.hcr_el2));
DEFINE(CPU_USER_PT_REGS, offsetof(struct kvm_cpu_context, regs));
DEFINE(CPU_ELR_EL2, offsetof(struct kvm_cpu_context, sys_regs[ELR_EL2]));
DEFINE(CPU_RGSR_EL1, offsetof(struct kvm_cpu_context, sys_regs[RGSR_EL1]));
DEFINE(CPU_GCR_EL1, offsetof(struct kvm_cpu_context, sys_regs[GCR_EL1]));
DEFINE(CPU_APIAKEYLO_EL1, offsetof(struct kvm_cpu_context, sys_regs[APIAKEYLO_EL1]));

8
arch/arm64/kvm/hyp/entry.S
View File

@ -83,6 +83,14 @@ alternative_else_nop_endif
eret
sb
SYM_INNER_LABEL(__guest_exit_restore_elr_and_panic, SYM_L_GLOBAL)
// x2-x29,lr: vcpu regs
// vcpu x0-x1 on the stack
adr_this_cpu x0, kvm_hyp_ctxt, x1
ldr x0, [x0, #CPU_ELR_EL2]
msr elr_el2, x0
SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)
// x2-x29,lr: vcpu regs
// vcpu x0-x1 on the stack

5
arch/arm64/kvm/hyp/include/hyp/switch.h
View File

@ -693,7 +693,7 @@ guest:
static inline void __kvm_unexpected_el2_exception(void)
{
extern char __guest_exit_panic[];
extern char __guest_exit_restore_elr_and_panic[];
unsigned long addr, fixup;
struct kvm_exception_table_entry *entry, *end;
unsigned long elr_el2 = read_sysreg(elr_el2);
@ -715,7 +715,8 @@ static inline void __kvm_unexpected_el2_exception(void)
}
/* Trigger a panic after restoring the hyp context. */
write_sysreg(__guest_exit_panic, elr_el2);
this_cpu_ptr(&kvm_hyp_ctxt)->sys_regs[ELR_EL2] = elr_el2;
write_sysreg(__guest_exit_restore_elr_and_panic, elr_el2);
}
#endif /* __ARM64_KVM_HYP_SWITCH_H__ */