From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
Dave Martin <Dave.Martin@arm.com>,
Weijiang Yang <weijiang.yang@intel.com>,
Pengfei Xu <pengfei.xu@intel.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: [PATCH v17 08/26] x86/mm: Introduce _PAGE_COW
Date: Tue, 29 Dec 2020 13:30:35 -0800 [thread overview]
Message-ID: <20201229213053.16395-9-yu-cheng.yu@intel.com> (raw)
In-Reply-To: <20201229213053.16395-1-yu-cheng.yu@intel.com>
There is essentially no room left in the x86 hardware PTEs on some OSes
(not Linux). That left the hardware architects looking for a way to
represent a new memory type (shadow stack) within the existing bits.
They chose to repurpose a lightly-used state: Write=0, Dirty=1.
The reason it's lightly used is that Dirty=1 is normally set by hardware
and cannot normally be set by hardware on a Write=0 PTE. Software must
normally be involved to create one of these PTEs, so software can simply
opt to not create them.
In places where Linux normally creates Write=0, Dirty=1, it can use the
software-defined _PAGE_COW in place of the hardware _PAGE_DIRTY. In other
words, whenever Linux needs to create Write=0, Dirty=1, it instead creates
Write=0, Cow=1, except for shadow stack, which is Write=0, Dirty=1. This
clearly separates shadow stack from other data, and results in the
following:
(a) A modified, copy-on-write (COW) page: (Write=0, Cow=1)
(b) A R/O page that has been COW'ed: (Write=0, Cow=1)
The user page is in a R/O VMA, and get_user_pages() needs a writable
copy. The page fault handler creates a copy of the page and sets
the new copy's PTE as Write=0 and Cow=1.
(c) A shadow stack PTE: (Write=0, Dirty=1)
(d) A shared shadow stack PTE: (Write=0, Cow=1)
When a shadow stack page is being shared among processes (this happens
at fork()), its PTE is made Dirty=0, so the next shadow stack access
causes a fault, and the page is duplicated and Dirty=1 is set again.
This is the COW equivalent for shadow stack pages, even though it's
copy-on-access rather than copy-on-write.
(e) A page where the processor observed a Write=1 PTE, started a write, set
Dirty=1, but then observed a Write=0 PTE. That's possible today, but
will not happen on processors that support shadow stack.
Define _PAGE_COW and update pte_*() helpers and apply the same changes to
pmd and pud.
After this, there are six free bits left in the 64-bit PTE, and no more
free bits in the 32-bit PTE (except for PAE) and Shadow Stack is not
implemented for the 32-bit kernel.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/include/asm/pgtable.h | 117 ++++++++++++++++++++++++---
arch/x86/include/asm/pgtable_types.h | 42 +++++++++-
2 files changed, 148 insertions(+), 11 deletions(-)
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index a02c67291cfc..61e4d3b17d87 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -121,9 +121,9 @@ extern pmdval_t early_pmd_flags;
* The following only work if pte_present() is true.
* Undefined behaviour if not..
*/
-static inline int pte_dirty(pte_t pte)
+static inline bool pte_dirty(pte_t pte)
{
- return pte_flags(pte) & _PAGE_DIRTY;
+ return pte_flags(pte) & _PAGE_DIRTY_BITS;
}
@@ -160,9 +160,9 @@ static inline int pte_young(pte_t pte)
return pte_flags(pte) & _PAGE_ACCESSED;
}
-static inline int pmd_dirty(pmd_t pmd)
+static inline bool pmd_dirty(pmd_t pmd)
{
- return pmd_flags(pmd) & _PAGE_DIRTY;
+ return pmd_flags(pmd) & _PAGE_DIRTY_BITS;
}
static inline int pmd_young(pmd_t pmd)
@@ -170,9 +170,9 @@ static inline int pmd_young(pmd_t pmd)
return pmd_flags(pmd) & _PAGE_ACCESSED;
}
-static inline int pud_dirty(pud_t pud)
+static inline bool pud_dirty(pud_t pud)
{
- return pud_flags(pud) & _PAGE_DIRTY;
+ return pud_flags(pud) & _PAGE_DIRTY_BITS;
}
static inline int pud_young(pud_t pud)
@@ -182,6 +182,12 @@ static inline int pud_young(pud_t pud)
static inline int pte_write(pte_t pte)
{
+ /*
+ * If _PAGE_DIRTY is set, the PTE must either have _PAGE_RW or be
+ * a shadow stack PTE, which is logically writable.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK))
+ return pte_flags(pte) & (_PAGE_RW | _PAGE_DIRTY);
return pte_flags(pte) & _PAGE_RW;
}
@@ -333,7 +339,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte)
static inline pte_t pte_mkclean(pte_t pte)
{
- return pte_clear_flags(pte, _PAGE_DIRTY);
+ return pte_clear_flags(pte, _PAGE_DIRTY_BITS);
}
static inline pte_t pte_mkold(pte_t pte)
@@ -343,6 +349,16 @@ static inline pte_t pte_mkold(pte_t pte)
static inline pte_t pte_wrprotect(pte_t pte)
{
+ /*
+ * Blindly clearing _PAGE_RW might accidentally create
+ * a shadow stack PTE (RW=0, Dirty=1). Move the hardware
+ * dirty value to the software bit.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ pte.pte |= (pte.pte & _PAGE_DIRTY) >> _PAGE_BIT_DIRTY << _PAGE_BIT_COW;
+ pte = pte_clear_flags(pte, _PAGE_DIRTY);
+ }
+
return pte_clear_flags(pte, _PAGE_RW);
}
@@ -353,6 +369,18 @@ static inline pte_t pte_mkexec(pte_t pte)
static inline pte_t pte_mkdirty(pte_t pte)
{
+ pteval_t dirty = _PAGE_DIRTY;
+
+ /* Avoid creating (HW)Dirty=1, Write=0 PTEs */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !pte_write(pte))
+ dirty = _PAGE_COW;
+
+ return pte_set_flags(pte, dirty | _PAGE_SOFT_DIRTY);
+}
+
+static inline pte_t pte_mkwrite_shstk(pte_t pte)
+{
+ pte = pte_clear_flags(pte, _PAGE_COW);
return pte_set_flags(pte, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
}
@@ -363,6 +391,13 @@ static inline pte_t pte_mkyoung(pte_t pte)
static inline pte_t pte_mkwrite(pte_t pte)
{
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ if (pte_flags(pte) & _PAGE_COW) {
+ pte = pte_clear_flags(pte, _PAGE_COW);
+ pte = pte_set_flags(pte, _PAGE_DIRTY);
+ }
+ }
+
return pte_set_flags(pte, _PAGE_RW);
}
@@ -434,16 +469,40 @@ static inline pmd_t pmd_mkold(pmd_t pmd)
static inline pmd_t pmd_mkclean(pmd_t pmd)
{
- return pmd_clear_flags(pmd, _PAGE_DIRTY);
+ return pmd_clear_flags(pmd, _PAGE_DIRTY_BITS);
}
static inline pmd_t pmd_wrprotect(pmd_t pmd)
{
+ /*
+ * Blindly clearing _PAGE_RW might accidentally create
+ * a shadow stack PMD (RW=0, Dirty=1). Move the hardware
+ * dirty value to the software bit.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ pmdval_t v = native_pmd_val(pmd);
+
+ v |= (v & _PAGE_DIRTY) >> _PAGE_BIT_DIRTY << _PAGE_BIT_COW;
+ pmd = pmd_clear_flags(__pmd(v), _PAGE_DIRTY);
+ }
+
return pmd_clear_flags(pmd, _PAGE_RW);
}
static inline pmd_t pmd_mkdirty(pmd_t pmd)
{
+ 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))
+ dirty = _PAGE_COW;
+
+ return pmd_set_flags(pmd, dirty | _PAGE_SOFT_DIRTY);
+}
+
+static inline pmd_t pmd_mkwrite_shstk(pmd_t pmd)
+{
+ pmd = pmd_clear_flags(pmd, _PAGE_COW);
return pmd_set_flags(pmd, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
}
@@ -464,6 +523,13 @@ static inline pmd_t pmd_mkyoung(pmd_t pmd)
static inline pmd_t pmd_mkwrite(pmd_t pmd)
{
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ if (pmd_flags(pmd) & _PAGE_COW) {
+ pmd = pmd_clear_flags(pmd, _PAGE_COW);
+ pmd = pmd_set_flags(pmd, _PAGE_DIRTY);
+ }
+ }
+
return pmd_set_flags(pmd, _PAGE_RW);
}
@@ -488,17 +554,35 @@ static inline pud_t pud_mkold(pud_t pud)
static inline pud_t pud_mkclean(pud_t pud)
{
- return pud_clear_flags(pud, _PAGE_DIRTY);
+ return pud_clear_flags(pud, _PAGE_DIRTY_BITS);
}
static inline pud_t pud_wrprotect(pud_t pud)
{
+ /*
+ * Blindly clearing _PAGE_RW might accidentally create
+ * a shadow stack PUD (RW=0, Dirty=1). Move the hardware
+ * dirty value to the software bit.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ pudval_t v = native_pud_val(pud);
+
+ v |= (v & _PAGE_DIRTY) >> _PAGE_BIT_DIRTY << _PAGE_BIT_COW;
+ pud = pud_clear_flags(__pud(v), _PAGE_DIRTY);
+ }
+
return pud_clear_flags(pud, _PAGE_RW);
}
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))
+ dirty = _PAGE_COW;
+
+ return pud_set_flags(pud, dirty | _PAGE_SOFT_DIRTY);
}
static inline pud_t pud_mkdevmap(pud_t pud)
@@ -518,6 +602,13 @@ static inline pud_t pud_mkyoung(pud_t pud)
static inline pud_t pud_mkwrite(pud_t pud)
{
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ if (pud_flags(pud) & _PAGE_COW) {
+ pud = pud_clear_flags(pud, _PAGE_COW);
+ pud = pud_set_flags(pud, _PAGE_DIRTY);
+ }
+ }
+
return pud_set_flags(pud, _PAGE_RW);
}
@@ -1131,6 +1222,12 @@ extern int pmdp_clear_flush_young(struct vm_area_struct *vma,
#define pmd_write pmd_write
static inline int pmd_write(pmd_t pmd)
{
+ /*
+ * If _PAGE_DIRTY is set, then the PMD must either have _PAGE_RW or
+ * be a shadow stack PMD, which is logically writable.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK))
+ return pmd_flags(pmd) & (_PAGE_RW | _PAGE_DIRTY);
return pmd_flags(pmd) & _PAGE_RW;
}
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index b8b79d618bbc..b02084a181c2 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -23,7 +23,8 @@
#define _PAGE_BIT_SOFTW2 10 /* " */
#define _PAGE_BIT_SOFTW3 11 /* " */
#define _PAGE_BIT_PAT_LARGE 12 /* On 2MB or 1GB pages */
-#define _PAGE_BIT_SOFTW4 58 /* available for programmer */
+#define _PAGE_BIT_SOFTW4 57 /* available for programmer */
+#define _PAGE_BIT_SOFTW5 58 /* available for programmer */
#define _PAGE_BIT_PKEY_BIT0 59 /* Protection Keys, bit 1/4 */
#define _PAGE_BIT_PKEY_BIT1 60 /* Protection Keys, bit 2/4 */
#define _PAGE_BIT_PKEY_BIT2 61 /* Protection Keys, bit 3/4 */
@@ -36,6 +37,15 @@
#define _PAGE_BIT_SOFT_DIRTY _PAGE_BIT_SOFTW3 /* software dirty tracking */
#define _PAGE_BIT_DEVMAP _PAGE_BIT_SOFTW4
+/*
+ * Indicates a copy-on-write page.
+ */
+#ifdef CONFIG_X86_CET_USER
+#define _PAGE_BIT_COW _PAGE_BIT_SOFTW5 /* copy-on-write */
+#else
+#define _PAGE_BIT_COW 0
+#endif
+
/* If _PAGE_BIT_PRESENT is clear, we use these: */
/* - if the user mapped it with PROT_NONE; pte_present gives true */
#define _PAGE_BIT_PROTNONE _PAGE_BIT_GLOBAL
@@ -117,6 +127,36 @@
#define _PAGE_DEVMAP (_AT(pteval_t, 0))
#endif
+/*
+ * The hardware requires shadow stack to be read-only and Dirty.
+ * _PAGE_COW is a software-only bit used to separate copy-on-write PTEs
+ * from shadow stack PTEs:
+ * (a) A modified, copy-on-write (COW) page: (Write=0, Cow=1)
+ * (b) A R/O page that has been COW'ed: (Write=0, Cow=1)
+ * The user page is in a R/O VMA, and get_user_pages() needs a
+ * writable copy. The page fault handler creates a copy of the page
+ * and sets the new copy's PTE as Write=0, Cow=1.
+ * (c) A shadow stack PTE: (Write=0, Dirty=1)
+ * (d) A shared (copy-on-access) shadow stack PTE: (Write=0, Cow=1)
+ * When a shadow stack page is being shared among processes (this
+ * happens at fork()), its PTE is cleared of _PAGE_DIRTY, so the next
+ * shadow stack access causes a fault, and the page is duplicated and
+ * _PAGE_DIRTY is set again. This is the COW equivalent for shadow
+ * stack pages, even though it's copy-on-access rather than
+ * copy-on-write.
+ * (e) A page where the processor observed a Write=1 PTE, started a write,
+ * set Dirty=1, but then observed a Write=0 PTE (changed by another
+ * thread). That's possible today, but will not happen on processors
+ * that support shadow stack.
+ */
+#ifdef CONFIG_X86_CET_USER
+#define _PAGE_COW (_AT(pteval_t, 1) << _PAGE_BIT_COW)
+#else
+#define _PAGE_COW (_AT(pteval_t, 0))
+#endif
+
+#define _PAGE_DIRTY_BITS (_PAGE_DIRTY | _PAGE_COW)
+
#define _PAGE_PROTNONE (_AT(pteval_t, 1) << _PAGE_BIT_PROTNONE)
/*
--
2.21.0
next prev parent reply other threads:[~2020-12-29 21:33 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-29 21:30 [PATCH v17 00/26] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 01/26] Documentation/x86: Add CET description Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 02/26] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection Yu-cheng Yu
2021-01-19 11:06 ` Borislav Petkov
2021-01-19 18:10 ` Yu, Yu-cheng
2020-12-29 21:30 ` [PATCH v17 03/26] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 04/26] x86/cpufeatures: Introduce X86_FEATURE_CET and setup functions Yu-cheng Yu
2021-01-11 17:56 ` Borislav Petkov
2021-01-11 20:25 ` Yu, Yu-cheng
2021-01-11 23:09 ` Yu-cheng Yu
2021-01-12 0:09 ` Yu, Yu-cheng
2021-01-12 12:38 ` Borislav Petkov
2021-01-12 23:02 ` Yu, Yu-cheng
2021-01-13 10:04 ` Borislav Petkov
2020-12-29 21:30 ` [PATCH v17 05/26] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 06/26] x86/cet: Add control-protection fault handler Yu-cheng Yu
2021-01-19 12:04 ` Borislav Petkov
2021-01-19 19:36 ` Yu, Yu-cheng
2020-12-29 21:30 ` [PATCH v17 07/26] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Yu-cheng Yu
2020-12-29 21:30 ` Yu-cheng Yu [this message]
2021-01-21 18:44 ` [PATCH v17 08/26] x86/mm: Introduce _PAGE_COW Borislav Petkov
2021-01-21 20:16 ` Yu, Yu-cheng
2021-01-21 20:20 ` Dave Hansen
2021-01-21 20:26 ` Dave Hansen
2021-01-21 20:44 ` Yu, Yu-cheng
2021-01-21 20:41 ` Borislav Petkov
2021-01-21 21:40 ` Yu, Yu-cheng
2021-01-21 22:16 ` David Laight
2021-01-21 22:19 ` Randy Dunlap
2021-01-21 22:32 ` David Laight
2021-01-22 21:54 ` Yu, Yu-cheng
2020-12-29 21:30 ` [PATCH v17 09/26] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 10/26] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 11/26] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Yu-cheng Yu
2021-01-25 18:27 ` Borislav Petkov
2021-01-25 21:27 ` Yu, Yu-cheng
2021-01-25 21:55 ` Borislav Petkov
2021-01-25 22:18 ` Yu, Yu-cheng
2021-01-26 10:24 ` Borislav Petkov
2021-01-26 16:45 ` Yu, Yu-cheng
2021-01-26 8:46 ` Peter Zijlstra
2021-01-26 9:40 ` Peter Zijlstra
2021-01-26 16:43 ` Yu, Yu-cheng
2020-12-29 21:30 ` [PATCH v17 12/26] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 13/26] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 14/26] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 15/26] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 16/26] mm: Add guard pages around a shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 17/26] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 18/26] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 19/26] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 20/26] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 21/26] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 22/26] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND properties Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 23/26] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 24/26] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 25/26] x86/cet/shstk: Add arch_prctl functions for " Yu-cheng Yu
2020-12-29 21:30 ` [PATCH v17 26/26] mm: Introduce PROT_SHSTK " Yu-cheng Yu
2021-01-04 20:08 ` [PATCH v17 00/26] Control-flow Enforcement: Shadow Stack Yu, Yu-cheng
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