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The subsequent instruction read will fault >>> and it adds to the overhead. Currently exec-only mappings are not >>> widespread but I heard some people planning to move in this direction as >>> a default build configuration. >> I tested exec-only on QEMU tcg, but I don't have a hardware supported EPAN. >> I don't think performance benchmark on QEMU tcg makes sense since it is >> quite slow, such small overhead is unlikely measurable on it. > Yeah, benchmarking under qemu is pointless. I think you can remove some > of the ARM64_HAS_EPAN checks (or replaced them with ARM64_HAS_PAN) just > for testing. For security reason, we removed this behaviour in commit > 24cecc377463 ("arm64: Revert support for execute-only user mappings") > but it's good enough for testing. This should give you PROT_EXEC-only > mappings on your hardware. Thanks for the suggestion. IIUC, I still can emulate exec-only even though hardware doesn't support EPAN? So it means reading exec-only area in kernel still can trigger fault, right? And 24cecc377463 ("arm64: Revert support for execute-only user mappings") can't be reverted cleanly by git revert, so I did it manually as below. diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 6a8b71917e3b..0bdedd415e56 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -573,8 +573,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,                 /* Write implies read */                 vm_flags |= VM_WRITE;                 /* If EPAN is absent then exec implies read */ -               if (!alternative_has_cap_unlikely(ARM64_HAS_EPAN)) -                       vm_flags |= VM_EXEC; +               //if (!alternative_has_cap_unlikely(ARM64_HAS_EPAN)) +               //      vm_flags |= VM_EXEC;         }         if (is_ttbr0_addr(addr) && is_el1_permission_fault(addr, esr, regs)) { diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c index 642bdf908b22..d30265d424e4 100644 --- a/arch/arm64/mm/mmap.c +++ b/arch/arm64/mm/mmap.c @@ -19,7 +19,7 @@ static pgprot_t protection_map[16] __ro_after_init = {         [VM_WRITE]                                      = PAGE_READONLY,         [VM_WRITE | VM_READ]                            = PAGE_READONLY,         /* PAGE_EXECONLY if Enhanced PAN */ -       [VM_EXEC]                                       = PAGE_READONLY_EXEC, +       [VM_EXEC]                                       = PAGE_EXECONLY,         [VM_EXEC | VM_READ]                             = PAGE_READONLY_EXEC,         [VM_EXEC | VM_WRITE]                            = PAGE_READONLY_EXEC,         [VM_EXEC | VM_WRITE | VM_READ]                  = PAGE_READONLY_EXEC, Is it correct? Just wanted to make sure I did the right thing before running test. >