Re: [PATCH 19/35] mm/mmap: Add shadow stack pages to memory accounting
From: Dave Hansen <hidden>
Date: 2022-02-09 22:28:57
Also in:
linux-arch, linux-doc, linux-mm, lkml
On 1/30/22 13:18, Rick Edgecombe wrote:
quoted hunk ↗ jump to hunk
+bool is_shadow_stack_mapping(vm_flags_t vm_flags) +{ + return vm_flags & VM_SHADOW_STACK; +}diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index bc8713a76e03..21fdb1273571 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h@@ -911,6 +911,14 @@ static inline void ptep_modify_prot_commit(struct vm_area_struct *vma, __ptep_modify_prot_commit(vma, addr, ptep, pte); } #endif /* __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION */ + +#ifndef is_shadow_stack_mapping +static inline bool is_shadow_stack_mapping(vm_flags_t vm_flags) +{ + return false; +} +#endif
Hold your horses there. Remember:
+#ifdef CONFIG_X86_SHADOW_STACK
+# define VM_SHADOW_STACK VM_HIGH_ARCH_5
+#else
+# define VM_SHADOW_STACK VM_NONE
+#endif
Plus:
#define VM_NONE 0x00000000
That means the arch-generic version, when CONFIG_X86_SHADOW_STACK is off
compiles down to:
bool is_shadow_stack_mapping(vm_flags_t vm_flags)
{
return vm_flags & 0x00000000;
}
I _suspect_ the compiler *might* compile that down to the same thing as:
return false;
So, why not just have one version, no additional #ifdefs, and be done
with it? Heck, why have the helper in the first place? Just check
VM_SHADOW_STACK directly.