[PATCH v2 08/39] x86/mm: Remove _PAGE_DIRTY from kernel RO pages

Rick Edgecombe
2022-09-29T22:30:50Z

From: Yu-cheng Yu <yu-cheng.yu@intel.com>

Processors sometimes directly create Write=0,Dirty=1 PTEs. These PTEs are
created by software. One such case is that kernel read-only pages are
historically set up as Dirty.

New processors that support Shadow Stack regard Write=0,Dirty=1 PTEs as
shadow stack pages. When CR4.CET=1 and IA32_S_CET.SH_STK_EN=1, some
instructions can write to such supervisor memory. The kernel does not set
IA32_S_CET.SH_STK_EN, but to reduce ambiguity between shadow stack and
regular Write=0 pages, removed Dirty=1 from any kernel Write=0 PTEs.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>

---

v2:
- Normalize PTE bit descriptions between patches

arch/x86/include/asm/pgtable_types.h | 6 +++---
arch/x86/mm/pat/set_memory.c | 2 +-
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index aa174fed3a71..ff82237e7b6b 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -192,10 +192,10 @@ enum page_cache_mode {
#define _KERNPG_TABLE (__PP|__RW| 0|___A| 0|___D| 0| 0| _ENC)
#define _PAGE_TABLE_NOENC (__PP|__RW|_USR|___A| 0|___D| 0| 0)
#define _PAGE_TABLE (__PP|__RW|_USR|___A| 0|___D| 0| 0| _ENC)
-#define __PAGE_KERNEL_RO (__PP| 0| 0|___A|__NX|___D| 0|___G)
-#define __PAGE_KERNEL_ROX (__PP| 0| 0|___A| 0|___D| 0|___G)
+#define __PAGE_KERNEL_RO (__PP| 0| 0|___A|__NX| 0| 0|___G)
+#define __PAGE_KERNEL_ROX (__PP| 0| 0|___A| 0| 0| 0|___G)
#define __PAGE_KERNEL_NOCACHE (__PP|__RW| 0|___A|__NX|___D| 0|___G| __NC)
-#define __PAGE_KERNEL_VVAR (__PP| 0|_USR|___A|__NX|___D| 0|___G)
+#define __PAGE_KERNEL_VVAR (__PP| 0|_USR|___A|__NX| 0| 0|___G)
#define __PAGE_KERNEL_LARGE (__PP|__RW| 0|___A|__NX|___D|_PSE|___G)
#define __PAGE_KERNEL_LARGE_EXEC (__PP|__RW| 0|___A| 0|___D|_PSE|___G)
#define __PAGE_KERNEL_WP (__PP|__RW| 0|___A|__NX|___D| 0|___G| __WP)
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 1abd5438f126..ed9193b469ba 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1977,7 +1977,7 @@ int set_memory_nx(unsigned long addr, int numpages)

int set_memory_ro(unsigned long addr, int numpages)
{
- return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW), 0);
+ return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW | _PAGE_DIRTY), 0);
}

int set_memory_rw(unsigned long addr, int numpages)
--
2.17.1