On Thu, Aug 22, 2024 at 02:15:22AM +0100, Mark Brown wrote:
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 451ba7cbd5ad..3ada31c2ac12 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -486,6 +486,14 @@ static void do_bad_area(unsigned long far, unsigned long esr, } } +static bool is_gcs_fault(unsigned long esr) +{
- if (!esr_is_data_abort(esr))
return false;- return ESR_ELx_ISS2(esr) & ESR_ELx_GCS;
+}
static bool is_el0_instruction_abort(unsigned long esr) { return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_LOW; @@ -500,6 +508,23 @@ static bool is_write_abort(unsigned long esr) return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM); } +static bool is_invalid_gcs_access(struct vm_area_struct *vma, u64 esr) +{
- if (!system_supports_gcs())
return false;- if (unlikely(is_gcs_fault(esr))) {
/* GCS accesses must be performed on a GCS page */if (!(vma->vm_flags & VM_SHADOW_STACK))return true;
This first check covers the GCSPOPM/RET etc. permission faults on non-GCS vmas. It looks correct.
- } else if (unlikely(vma->vm_flags & VM_SHADOW_STACK)) {
/* Only GCS operations can write to a GCS page */return is_write_abort(esr);- }
I don't think that's right. The ESR on this path may not even indicate a data abort and ESR.WnR bit check wouldn't make sense.
I presume we want to avoid an infinite loop on a (writeable) GCS page when the user does a normal STR but the CPU raises a permission fault. I think this function needs to just return false if !esr_is_data_abort().
- return false;
+}
static int __kprobes do_page_fault(unsigned long far, unsigned long esr, struct pt_regs *regs) { @@ -535,6 +560,14 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, /* It was exec fault */ vm_flags = VM_EXEC; mm_flags |= FAULT_FLAG_INSTRUCTION;
- } else if (is_gcs_fault(esr)) {
/** The GCS permission on a page implies both read and* write so always handle any GCS fault as a write fault,* we need to trigger CoW even for GCS reads.*/vm_flags = VM_WRITE;mm_flags |= FAULT_FLAG_WRITE;@@ -568,6 +601,13 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, if (!vma) goto lock_mmap;
- if (is_invalid_gcs_access(vma, esr)) {
vma_end_read(vma);fault = 0;si_code = SEGV_ACCERR;goto bad_area;- }
Here there's a risk that the above function returns true for some unrelated fault that happens to have bit 6 in ESR set.