From: Deepak Gupta <debug@rivosinc.com>
To: paul.walmsley@sifive.com, rick.p.edgecombe@intel.com,
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Subject: [PATCH v3 13/29] riscv mmu: write protect and shadow stack
Date: Wed, 3 Apr 2024 16:35:01 -0700 [thread overview]
Message-ID: <20240403234054.2020347-14-debug@rivosinc.com> (raw)
In-Reply-To: <20240403234054.2020347-1-debug@rivosinc.com>
`fork` implements copy on write (COW) by making pages readonly in child
and parent both.
ptep_set_wrprotect and pte_wrprotect clears _PAGE_WRITE in PTE.
Assumption is that page is readable and on fault copy on write happens.
To implement COW on such pages, clearing up W bit makes them XWR = 000.
This will result in wrong PTE setting which says no perms but V=1 and PFN
field pointing to final page. Instead desired behavior is to turn it into
a readable page, take an access (load/store) fault on sspush/sspop
(shadow stack) and then perform COW on such pages. This way regular reads
would still be allowed and not lead to COW maintaining current behavior
of COW on non-shadow stack but writeable memory.
On the other hand it doesn't interfere with existing COW for read-write
memory. Assumption is always that _PAGE_READ must have been set and thus
setting _PAGE_READ is harmless.
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
arch/riscv/include/asm/pgtable.h | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 9b837239d3e8..7a1c2a98d272 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -398,7 +398,7 @@ static inline int pte_special(pte_t pte)
static inline pte_t pte_wrprotect(pte_t pte)
{
- return __pte(pte_val(pte) & ~(_PAGE_WRITE));
+ return __pte((pte_val(pte) & ~(_PAGE_WRITE)) | (_PAGE_READ));
}
/* static inline pte_t pte_mkread(pte_t pte) */
@@ -581,7 +581,15 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
static inline void ptep_set_wrprotect(struct mm_struct *mm,
unsigned long address, pte_t *ptep)
{
- atomic_long_and(~(unsigned long)_PAGE_WRITE, (atomic_long_t *)ptep);
+ volatile pte_t read_pte = *ptep;
+ /*
+ * ptep_set_wrprotect can be called for shadow stack ranges too.
+ * shadow stack memory is XWR = 010 and thus clearing _PAGE_WRITE will lead to
+ * encoding 000b which is wrong encoding with V = 1. This should lead to page fault
+ * but we dont want this wrong configuration to be set in page tables.
+ */
+ atomic_long_set((atomic_long_t *)ptep,
+ ((pte_val(read_pte) & ~(unsigned long)_PAGE_WRITE) | _PAGE_READ));
}
#define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
--
2.43.2
next prev parent reply other threads:[~2024-04-03 23:42 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-03 23:34 [PATCH v3 00/29] riscv control-flow integrity for usermode Deepak Gupta
2024-04-03 23:34 ` [PATCH v3 01/29] riscv: envcfg save and restore on task switching Deepak Gupta
2024-05-09 0:10 ` Charlie Jenkins
2024-05-09 19:00 ` Deepak Gupta
2024-04-03 23:34 ` [PATCH v3 02/29] riscv: define default value for envcfg for task Deepak Gupta
2024-05-10 22:33 ` Charlie Jenkins
2024-05-13 18:33 ` Deepak Gupta
2024-04-03 23:34 ` [PATCH v3 03/29] riscv/Kconfig: enable HAVE_EXIT_THREAD for riscv Deepak Gupta
2024-05-10 22:36 ` Charlie Jenkins
2024-04-03 23:34 ` [PATCH v3 04/29] riscv: zicfilp / zicfiss in dt-bindings (extensions.yaml) Deepak Gupta
2024-04-10 11:58 ` Rob Herring
2024-04-10 21:37 ` Deepak Gupta
2024-04-15 19:41 ` Rob Herring
2024-04-16 15:44 ` Deepak Gupta
2024-05-09 18:14 ` Conor Dooley
2024-05-09 18:46 ` Deepak Gupta
2024-05-09 20:32 ` Conor Dooley
2024-05-09 23:26 ` Deepak Gupta
2024-04-03 23:34 ` [PATCH v3 05/29] riscv: zicfiss / zicfilp enumeration Deepak Gupta
2024-05-09 0:00 ` Andy Chiu
2024-05-09 0:07 ` Charlie Jenkins
2024-04-03 23:34 ` [PATCH v3 06/29] riscv: zicfiss / zicfilp extension csr and bit definitions Deepak Gupta
2024-05-10 22:37 ` Charlie Jenkins
2024-04-03 23:34 ` [PATCH v3 07/29] riscv: usercfi state for task and save/restore of CSR_SSP on trap entry/exit Deepak Gupta
2024-05-10 22:51 ` Charlie Jenkins
2024-04-03 23:34 ` [PATCH v3 08/29] mm: Define VM_SHADOW_STACK for RISC-V Deepak Gupta
2024-04-04 18:58 ` David Hildenbrand
2024-04-04 19:04 ` Mark Brown
2024-04-04 19:15 ` David Hildenbrand
2024-04-04 19:21 ` Deepak Gupta
2024-04-03 23:34 ` [PATCH v3 09/29] mm: abstract shadow stack vma behind `vma_is_shadow_stack` Deepak Gupta
2024-04-04 19:02 ` David Hildenbrand
2024-04-04 21:39 ` Deepak Gupta
2024-04-03 23:34 ` [PATCH v3 10/29] riscv/mm : ensure PROT_WRITE leads to VM_READ | VM_WRITE Deepak Gupta
2024-05-10 21:02 ` Charlie Jenkins
2024-05-13 17:47 ` Deepak Gupta
2024-05-13 18:36 ` Charlie Jenkins
2024-05-13 18:41 ` Deepak Gupta
2024-05-13 21:26 ` Charlie Jenkins
2024-05-12 16:24 ` Alexandre Ghiti
2024-05-13 18:29 ` Deepak Gupta
2024-04-03 23:34 ` [PATCH v3 11/29] riscv mm: manufacture shadow stack pte Deepak Gupta
2024-05-12 16:26 ` Alexandre Ghiti
2024-04-03 23:35 ` [PATCH v3 12/29] riscv mmu: teach pte_mkwrite to manufacture shadow stack PTEs Deepak Gupta
2024-05-12 16:28 ` Alexandre Ghiti
2024-05-13 17:33 ` Deepak Gupta
2024-04-03 23:35 ` Deepak Gupta [this message]
2024-05-12 16:31 ` [PATCH v3 13/29] riscv mmu: write protect and shadow stack Alexandre Ghiti
2024-05-13 17:32 ` Deepak Gupta
2024-05-23 14:59 ` Alexandre Ghiti
2024-05-24 7:16 ` Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 14/29] riscv/mm: Implement map_shadow_stack() syscall Deepak Gupta
2024-05-12 16:50 ` Alexandre Ghiti
2024-05-13 17:25 ` Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 15/29] riscv/shstk: If needed allocate a new shadow stack on clone Deepak Gupta
2024-05-12 17:05 ` Alexandre Ghiti
2024-05-13 17:10 ` Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 16/29] prctl: arch-agnostic prctl for shadow stack Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 17/29] prctl: arch-agnostic prctl for indirect branch tracking Deepak Gupta
2024-05-10 23:29 ` Charlie Jenkins
2024-05-13 18:31 ` Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 18/29] riscv: Implements arch agnostic shadow stack prctls Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 19/29] riscv: Implements arch agnostic indirect branch tracking prctls Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 20/29] riscv/kernel: update __show_regs to print shadow stack register Deepak Gupta
2024-05-12 17:10 ` Alexandre Ghiti
2024-04-03 23:35 ` [PATCH v3 21/29] riscv/traps: Introduce software check exception Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 22/29] riscv sigcontext: adding cfi state field in sigcontext Deepak Gupta
2024-05-24 9:46 ` Andy Chiu
2024-05-24 19:11 ` Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 23/29] riscv signal: Save and restore of shadow stack for signal Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 24/29] riscv/ptrace: riscv cfi status and state via ptrace and in core files Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 25/29] riscv/hwprobe: zicfilp / zicfiss enumeration in hwprobe Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 26/29] riscv: create a config for shadow stack and landing pad instr support Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 27/29] riscv: Documentation for landing pad / indirect branch tracking Deepak Gupta
2024-05-10 20:30 ` Charlie Jenkins
2024-05-13 17:07 ` Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 28/29] riscv: Documentation for shadow stack on riscv Deepak Gupta
2024-04-03 23:35 ` [PATCH v3 29/29] kselftest/riscv: kselftest for user mode cfi Deepak Gupta
2024-05-09 18:21 ` Charlie Jenkins
2024-05-09 19:16 ` Deepak Gupta
2024-05-10 1:20 ` Charlie Jenkins
2024-05-09 0:33 ` [PATCH v3 00/29] riscv control-flow integrity for usermode Charlie Jenkins
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