This is a note to let you know that I've just added the patch titled KVM: arm64: Survive synchronous exceptions caused by AT instructions to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-arm64-survive-synchronous-exceptions-caused-by-at-instructions.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Sep 8 03:15:18 PM CEST 2020 From: Andre Przywara <andre.przywara@xxxxxxx> Date: Fri, 4 Sep 2020 12:24:36 +0100 Subject: KVM: arm64: Survive synchronous exceptions caused by AT instructions To: stable@xxxxxxxxxxxxxxx Cc: James Morse <james.morse@xxxxxxx>, Marc Zyngier <maz@xxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx> Message-ID: <20200904112437.200212-4-andre.przywara@xxxxxxx> From: James Morse <james.morse@xxxxxxx> 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@xxxxxxxxxxxxxxx # v4.14 Signed-off-by: James Morse <james.morse@xxxxxxx> Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -83,6 +83,34 @@ 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 @@ -207,6 +207,15 @@ 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]! @@ -244,7 +253,6 @@ 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_sync_invalid @@ -261,7 +269,7 @@ ENTRY(__kvm_hyp_vector) ventry el2t_fiq_invalid // FIQ EL2t ventry el2t_error_invalid // Error EL2t - ventry el2h_sync_invalid // Synchronous EL2h + ventry el2_sync // Synchronous EL2h ventry el2h_irq_invalid // IRQ EL2h ventry el2h_fiq_invalid // FIQ EL2h ventry el2_error // Error EL2h --- a/arch/arm64/kvm/hyp/switch.c +++ b/arch/arm64/kvm/hyp/switch.c @@ -220,10 +220,10 @@ 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)) Patches currently in stable-queue which might be from andre.przywara@xxxxxxx are queue-4.14/kvm-arm64-set-hcr_el2.ptw-to-prevent-at-taking-synchronous-exception.patch queue-4.14/kvm-arm64-survive-synchronous-exceptions-caused-by-at-instructions.patch queue-4.14/kvm-arm64-defer-guest-entry-when-an-asynchronous-exception-is-pending.patch queue-4.14/kvm-arm64-add-kvm_extable-for-vaxorcism-code.patch