Re: [PATCH v4 17/36] arm64/mm: Handle GCS data aborts
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2023-08-11 15:09:45
Also in:
kvmarm, linux-arch, linux-arm-kernel, linux-fsdevel, linux-kselftest, linux-mm, linux-riscv, lkml
On Mon, Aug 07, 2023 at 11:00:22PM +0100, Mark Brown wrote:
quoted hunk ↗ jump to hunk
@@ -510,6 +527,26 @@ static vm_fault_t __do_page_fault(struct mm_struct *mm, */ if (!(vma->vm_flags & vm_flags)) return VM_FAULT_BADACCESS; + + if (vma->vm_flags & VM_SHADOW_STACK) { + /* + * Writes to a GCS must either be generated by a GCS + * operation or be from EL1. + */ + if (is_write_abort(esr) && + !(is_gcs_fault(esr) || is_el1_data_abort(esr))) + return VM_FAULT_BADACCESS;
Related to my PIE permissions comment: when do we have a valid EL1 data write abort that's not a GCS fault? Does a faulting GCSSTTR set the ESR_ELx_GCS bit?
quoted hunk ↗ jump to hunk
+ } else { + /* + * GCS faults should never happen for pages that are + * not part of a GCS and the operation being attempted + * can never succeed. + */ + if (is_gcs_fault(esr)) + return VM_FAULT_BADACCESS;
If one does a GCS push/store to a non-GCS page, do we get a GCS fault or something else? I couldn't figure out from the engineering spec. If the hardware doesn't generate such exceptions, we might as well remove this 'else' branch. But maybe it does generate a GCS-specific fault as you added a similar check in is_invalid_el0_gcs_access().
quoted hunk ↗ jump to hunk
@@ -595,6 +644,19 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, if (!vma) goto lock_mmap; + /* + * We get legitimate write faults for GCS pages from GCS + * operations and from EL1 writes to EL0 pages but just plain
What are the EL1 writes to the shadow stack? Would it not use copy_to_user_gcs()? -- Catalin