[tip: x86/shstk] x86/mm: Teach pte_mkwrite() about stack memory

From: tip-bot2 for Rick Edgecombe
Date: Fri Jun 16 2023 - 15:18:32 EST


The following commit has been merged into the x86/shstk branch of tip:

Commit-ID: d3ffcb4e9599461daf567a0ac3ecebe7e09142d3
Gitweb: https://git.kernel.org/tip/d3ffcb4e9599461daf567a0ac3ecebe7e09142d3
Author: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
AuthorDate: Mon, 12 Jun 2023 17:10:47 -07:00
Committer: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Thu, 15 Jun 2023 16:31:33 -07:00

x86/mm: Teach pte_mkwrite() about stack memory

If a VMA has the VM_SHADOW_STACK flag, it is shadow stack memory. So
when it is made writable with pte_mkwrite(), it should create shadow
stack memory, not conventionally writable memory. Now that all the places
where shadow stack memory might be created pass a VMA into pte_mkwrite(),
it can know when it should do this.

So make pte_mkwrite() create shadow stack memory when the VMA has the
VM_SHADOW_STACK flag. Do the same thing for pmd_mkwrite().

This requires referencing VM_SHADOW_STACK in these functions, which are
currently defined in pgtable.h, however mm.h (where VM_SHADOW_STACK is
located) can't be pulled in without causing problems for files that
reference pgtable.h. So also move pte/pmd_mkwrite() into pgtable.c, where
they can safely reference VM_SHADOW_STACK.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Acked-by: Deepak Gupta <debug@xxxxxxxxxxxx>
Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Tested-by: John Allen <john.allen@xxxxxxx>
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20230613001108.3040476-22-rick.p.edgecombe%40intel.com
---
arch/x86/mm/pgtable.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 101e721..c4b222d 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -883,6 +883,9 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)

pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma)
{
+ if (vma->vm_flags & VM_SHADOW_STACK)
+ return pte_mkwrite_shstk(pte);
+
pte = pte_mkwrite_novma(pte);

return pte_clear_saveddirty(pte);
@@ -890,6 +893,9 @@ pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma)

pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
{
+ if (vma->vm_flags & VM_SHADOW_STACK)
+ return pmd_mkwrite_shstk(pmd);
+
pmd = pmd_mkwrite_novma(pmd);

return pmd_clear_saveddirty(pmd);