From: James Morse james.morse@arm.com
commit 88a84ccccb3966bcc3f309cdb76092a9892c0260 upstream.
KVM doesn't expect any synchronous exceptions when executing, any such exception leads to a panic(). AT instructions access the guest page tables, and can cause a synchronous external abort to be taken.
The arm-arm is unclear on what should happen if the guest has configured the hardware update of the access-flag, and a memory type in TCR_EL1 that does not support atomic operations. B2.2.6 "Possible implementation restrictions on using atomic instructions" from DDI0487F.a lists synchronous external abort as a possible behaviour of atomic instructions that target memory that isn't writeback cacheable, but the page table walker may behave differently.
Make KVM robust to synchronous exceptions caused by AT instructions. Add a get_user() style helper for AT instructions that returns -EFAULT if an exception was generated.
While KVM's version of the exception table mixes synchronous and asynchronous exceptions, only one of these can occur at each location.
Re-enter the guest when the AT instructions take an exception on the assumption the guest will take the same exception. This isn't guaranteed to make forward progress, as the AT instructions may always walk the page tables, but guest execution may use the translation cached in the TLB.
This isn't a problem, as since commit 5dcd0fdbb492 ("KVM: arm64: Defer guest entry when an asynchronous exception is pending"), KVM will return to the host to process IRQs allowing the rest of the system to keep running.
Cc: stable@vger.kernel.org # v4.19 Signed-off-by: James Morse james.morse@arm.com Reviewed-by: Marc Zyngier maz@kernel.org Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Andre Przywara andre.przywara@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/kvm_asm.h | 28 ++++++++++++++++++++++++++++ arch/arm64/kvm/hyp/hyp-entry.S | 12 ++++++++++-- arch/arm64/kvm/hyp/switch.c | 8 ++++---- 3 files changed, 42 insertions(+), 6 deletions(-)
--- a/arch/arm64/include/asm/kvm_asm.h +++ b/arch/arm64/include/asm/kvm_asm.h @@ -87,6 +87,34 @@ extern u32 __init_stage2_translation(voi *__hyp_this_cpu_ptr(sym); \ })
+#define __KVM_EXTABLE(from, to) \ + " .pushsection __kvm_ex_table, "a"\n" \ + " .align 3\n" \ + " .long (" #from " - .), (" #to " - .)\n" \ + " .popsection\n" + + +#define __kvm_at(at_op, addr) \ +( { \ + int __kvm_at_err = 0; \ + u64 spsr, elr; \ + asm volatile( \ + " mrs %1, spsr_el2\n" \ + " mrs %2, elr_el2\n" \ + "1: at "at_op", %3\n" \ + " isb\n" \ + " b 9f\n" \ + "2: msr spsr_el2, %1\n" \ + " msr elr_el2, %2\n" \ + " mov %w0, %4\n" \ + "9:\n" \ + __KVM_EXTABLE(1b, 2b) \ + : "+r" (__kvm_at_err), "=&r" (spsr), "=&r" (elr) \ + : "r" (addr), "i" (-EFAULT)); \ + __kvm_at_err; \ +} ) + + #else /* __ASSEMBLY__ */
.macro hyp_adr_this_cpu reg, sym, tmp --- a/arch/arm64/kvm/hyp/hyp-entry.S +++ b/arch/arm64/kvm/hyp/hyp-entry.S @@ -186,6 +186,15 @@ el1_error: mov x0, #ARM_EXCEPTION_EL1_SERROR b __guest_exit
+el2_sync: + save_caller_saved_regs_vect + stp x29, x30, [sp, #-16]! + bl kvm_unexpected_el2_exception + ldp x29, x30, [sp], #16 + restore_caller_saved_regs_vect + + eret + el2_error: save_caller_saved_regs_vect stp x29, x30, [sp, #-16]! @@ -223,7 +232,6 @@ ENDPROC(\label) invalid_vector el2t_irq_invalid invalid_vector el2t_fiq_invalid invalid_vector el2t_error_invalid - invalid_vector el2h_sync_invalid invalid_vector el2h_irq_invalid invalid_vector el2h_fiq_invalid invalid_vector el1_fiq_invalid @@ -251,7 +259,7 @@ ENTRY(__kvm_hyp_vector) invalid_vect el2t_fiq_invalid // FIQ EL2t invalid_vect el2t_error_invalid // Error EL2t
- invalid_vect el2h_sync_invalid // Synchronous EL2h + valid_vect el2_sync // Synchronous EL2h invalid_vect el2h_irq_invalid // IRQ EL2h invalid_vect el2h_fiq_invalid // FIQ EL2h valid_vect el2_error // Error EL2h --- a/arch/arm64/kvm/hyp/switch.c +++ b/arch/arm64/kvm/hyp/switch.c @@ -268,10 +268,10 @@ static bool __hyp_text __translate_far_t * saved the guest context yet, and we may return early... */ par = read_sysreg(par_el1); - asm volatile("at s1e1r, %0" : : "r" (far)); - isb(); - - tmp = read_sysreg(par_el1); + if (!__kvm_at("s1e1r", far)) + tmp = read_sysreg(par_el1); + else + tmp = 1; /* back to the guest */ write_sysreg(par, par_el1);
if (unlikely(tmp & 1))