Re: [PATCH v21 08/26] x86/mm: Introduce _PAGE_COW
From: Borislav Petkov <bp@alien8.de>
Date: 2021-03-01 15:53:43
Also in:
linux-arch, linux-doc, linux-mm, lkml
On Wed, Feb 17, 2021 at 02:27:12PM -0800, Yu-cheng Yu wrote:
quoted hunk ↗ jump to hunk
@@ -182,7 +206,7 @@ static inline int pud_young(pud_t pud) static inline int pte_write(pte_t pte) { - return pte_flags(pte) & _PAGE_RW;
Put here a comment along the lines of: /* * Shadow stack pages are always writable - but not by normal * instructions but only by shadow stack operations. Therefore, the * W=0, D=1 test. */ to make it clear what this means.
quoted hunk ↗ jump to hunk
+ return (pte_flags(pte) & _PAGE_RW) || pte_shstk(pte); } static inline int pte_huge(pte_t pte)@@ -314,6 +338,24 @@ static inline pte_t pte_clear_flags(pte_t pte, pteval_t clear) return native_make_pte(v & ~clear); } +static inline pte_t pte_make_cow(pte_t pte)
pte_mkcow like the rest of the "pte_mkX" functions. And below too, for the other newly added pXd_make_* helpers.
static inline pmd_t pmd_mkdirty(pmd_t pmd)
{
- return pmd_set_flags(pmd, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
+ pmdval_t dirty = _PAGE_DIRTY;
+
+ /* Avoid creating (HW)Dirty=1, Write=0 PMDs */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !(pmd_flags(pmd) & _PAGE_RW))!(pmd_write(pmd))
+ dirty = _PAGE_COW; + + return pmd_set_flags(pmd, dirty | _PAGE_SOFT_DIRTY); +}
...
static inline pud_t pud_mkdirty(pud_t pud)
{
- return pud_set_flags(pud, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
+ pudval_t dirty = _PAGE_DIRTY;
+
+ /* Avoid creating (HW)Dirty=1, Write=0 PUDs */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !(pud_flags(pud) & _PAGE_RW))
!(pud_write(pud))
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette