[PATCH v4 17/29] arm64: implement PKEYS support
Joey Gouly
joey.gouly at arm.com
Fri May 3 06:01:35 PDT 2024
Implement the PKEYS interface, using the Permission Overlay Extension.
Signed-off-by: Joey Gouly <joey.gouly at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
---
arch/arm64/include/asm/mmu.h | 1 +
arch/arm64/include/asm/mmu_context.h | 51 ++++++++++++-
arch/arm64/include/asm/pgtable.h | 22 +++++-
arch/arm64/include/asm/pkeys.h | 110 +++++++++++++++++++++++++++
arch/arm64/include/asm/por.h | 33 ++++++++
arch/arm64/mm/mmu.c | 40 ++++++++++
6 files changed, 255 insertions(+), 2 deletions(-)
create mode 100644 arch/arm64/include/asm/pkeys.h
create mode 100644 arch/arm64/include/asm/por.h
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 65977c7783c5..983afeb4eba5 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -25,6 +25,7 @@ typedef struct {
refcount_t pinned;
void *vdso;
unsigned long flags;
+ u8 pkey_allocation_map;
} mm_context_t;
/*
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index c768d16b81a4..cb499db7a97b 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -15,12 +15,12 @@
#include <linux/sched/hotplug.h>
#include <linux/mm_types.h>
#include <linux/pgtable.h>
+#include <linux/pkeys.h>
#include <asm/cacheflush.h>
#include <asm/cpufeature.h>
#include <asm/daifflags.h>
#include <asm/proc-fns.h>
-#include <asm-generic/mm_hooks.h>
#include <asm/cputype.h>
#include <asm/sysreg.h>
#include <asm/tlbflush.h>
@@ -175,9 +175,36 @@ init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{
atomic64_set(&mm->context.id, 0);
refcount_set(&mm->context.pinned, 0);
+
+ /* pkey 0 is the default, so always reserve it. */
+ mm->context.pkey_allocation_map = 0x1;
+
+ return 0;
+}
+
+static inline void arch_dup_pkeys(struct mm_struct *oldmm,
+ struct mm_struct *mm)
+{
+ /* Duplicate the oldmm pkey state in mm: */
+ mm->context.pkey_allocation_map = oldmm->context.pkey_allocation_map;
+}
+
+static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
+{
+ arch_dup_pkeys(oldmm, mm);
+
return 0;
}
+static inline void arch_exit_mmap(struct mm_struct *mm)
+{
+}
+
+static inline void arch_unmap(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+}
+
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
static inline void update_saved_ttbr0(struct task_struct *tsk,
struct mm_struct *mm)
@@ -267,6 +294,28 @@ static inline unsigned long mm_untag_mask(struct mm_struct *mm)
return -1UL >> 8;
}
+/*
+ * We only want to enforce protection keys on the current process
+ * because we effectively have no access to POR_EL0 for other
+ * processes or any way to tell *which * POR_EL0 in a threaded
+ * process we could use.
+ *
+ * So do not enforce things if the VMA is not from the current
+ * mm, or if we are in a kernel thread.
+ */
+static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
+ bool write, bool execute, bool foreign)
+{
+ if (!arch_pkeys_enabled())
+ return true;
+
+ /* allow access if the VMA is not one from this process */
+ if (foreign || vma_is_foreign(vma))
+ return true;
+
+ return por_el0_allows_pkey(vma_pkey(vma), write, execute);
+}
+
#include <asm-generic/mmu_context.h>
#endif /* !__ASSEMBLY__ */
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 2449e4e27ea6..8ee68ff03016 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -34,6 +34,7 @@
#include <asm/cmpxchg.h>
#include <asm/fixmap.h>
+#include <asm/por.h>
#include <linux/mmdebug.h>
#include <linux/mm_types.h>
#include <linux/sched.h>
@@ -153,6 +154,24 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
#define pte_accessible(mm, pte) \
(mm_tlb_flush_pending(mm) ? pte_present(pte) : pte_valid(pte))
+static inline bool por_el0_allows_pkey(u8 pkey, bool write, bool execute)
+{
+ u64 por;
+
+ if (!system_supports_poe())
+ return true;
+
+ por = read_sysreg_s(SYS_POR_EL0);
+
+ if (write)
+ return por_elx_allows_write(por, pkey);
+
+ if (execute)
+ return por_elx_allows_exec(por, pkey);
+
+ return por_elx_allows_read(por, pkey);
+}
+
/*
* p??_access_permitted() is true for valid user mappings (PTE_USER
* bit set, subject to the write permission check). For execute-only
@@ -163,7 +182,8 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
#define pte_access_permitted_no_overlay(pte, write) \
(((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER)) && (!(write) || pte_write(pte)))
#define pte_access_permitted(pte, write) \
- pte_access_permitted_no_overlay(pte, write)
+ (pte_access_permitted_no_overlay(pte, write) && \
+ por_el0_allows_pkey(FIELD_GET(PTE_PO_IDX_MASK, pte_val(pte)), write, false))
#define pmd_access_permitted(pmd, write) \
(pte_access_permitted(pmd_pte(pmd), (write)))
#define pud_access_permitted(pud, write) \
diff --git a/arch/arm64/include/asm/pkeys.h b/arch/arm64/include/asm/pkeys.h
new file mode 100644
index 000000000000..a284508a4d02
--- /dev/null
+++ b/arch/arm64/include/asm/pkeys.h
@@ -0,0 +1,110 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023 Arm Ltd.
+ *
+ * Based on arch/x86/include/asm/pkeys.h
+ */
+
+#ifndef _ASM_ARM64_PKEYS_H
+#define _ASM_ARM64_PKEYS_H
+
+#define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2)
+
+#define arch_max_pkey() 7
+
+int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
+ unsigned long init_val);
+
+static inline bool arch_pkeys_enabled(void)
+{
+ return false;
+}
+
+static inline int vma_pkey(struct vm_area_struct *vma)
+{
+ return (vma->vm_flags & ARCH_VM_PKEY_FLAGS) >> VM_PKEY_SHIFT;
+}
+
+static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
+ int prot, int pkey)
+{
+ if (pkey != -1)
+ return pkey;
+
+ return vma_pkey(vma);
+}
+
+static inline int execute_only_pkey(struct mm_struct *mm)
+{
+ // Execute-only mappings are handled by EPAN/FEAT_PAN3.
+ WARN_ON_ONCE(!cpus_have_final_cap(ARM64_HAS_EPAN));
+
+ return -1;
+}
+
+#define mm_pkey_allocation_map(mm) (mm->context.pkey_allocation_map)
+#define mm_set_pkey_allocated(mm, pkey) do { \
+ mm_pkey_allocation_map(mm) |= (1U << pkey); \
+} while (0)
+#define mm_set_pkey_free(mm, pkey) do { \
+ mm_pkey_allocation_map(mm) &= ~(1U << pkey); \
+} while (0)
+
+static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
+{
+ /*
+ * "Allocated" pkeys are those that have been returned
+ * from pkey_alloc() or pkey 0 which is allocated
+ * implicitly when the mm is created.
+ */
+ if (pkey < 0)
+ return false;
+ if (pkey >= arch_max_pkey())
+ return false;
+
+ return mm_pkey_allocation_map(mm) & (1U << pkey);
+}
+
+/*
+ * Returns a positive, 3-bit key on success, or -1 on failure.
+ */
+static inline int mm_pkey_alloc(struct mm_struct *mm)
+{
+ /*
+ * Note: this is the one and only place we make sure
+ * that the pkey is valid as far as the hardware is
+ * concerned. The rest of the kernel trusts that
+ * only good, valid pkeys come out of here.
+ */
+ u8 all_pkeys_mask = ((1U << arch_max_pkey()) - 1);
+ int ret;
+
+ if (!arch_pkeys_enabled())
+ return -1;
+
+ /*
+ * Are we out of pkeys? We must handle this specially
+ * because ffz() behavior is undefined if there are no
+ * zeros.
+ */
+ if (mm_pkey_allocation_map(mm) == all_pkeys_mask)
+ return -1;
+
+ ret = ffz(mm_pkey_allocation_map(mm));
+
+ mm_set_pkey_allocated(mm, ret);
+
+ return ret;
+}
+
+static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
+{
+ if (!mm_pkey_is_allocated(mm, pkey))
+ return -EINVAL;
+
+ mm_set_pkey_free(mm, pkey);
+
+ return 0;
+}
+
+#endif /* _ASM_ARM64_PKEYS_H */
diff --git a/arch/arm64/include/asm/por.h b/arch/arm64/include/asm/por.h
new file mode 100644
index 000000000000..d6604e0c5c54
--- /dev/null
+++ b/arch/arm64/include/asm/por.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023 Arm Ltd.
+ */
+
+#ifndef _ASM_ARM64_POR_H
+#define _ASM_ARM64_POR_H
+
+#define POR_BITS_PER_PKEY 4
+#define POR_ELx_IDX(por_elx, idx) (((por_elx) >> (idx * POR_BITS_PER_PKEY)) & 0xf)
+
+static inline bool por_elx_allows_read(u64 por, u8 pkey)
+{
+ u8 perm = POR_ELx_IDX(por, pkey);
+
+ return perm & POE_R;
+}
+
+static inline bool por_elx_allows_write(u64 por, u8 pkey)
+{
+ u8 perm = POR_ELx_IDX(por, pkey);
+
+ return perm & POE_W;
+}
+
+static inline bool por_elx_allows_exec(u64 por, u8 pkey)
+{
+ u8 perm = POR_ELx_IDX(por, pkey);
+
+ return perm & POE_X;
+}
+
+#endif /* _ASM_ARM64_POR_H */
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 495b732d5af3..e50ccc86d150 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -25,6 +25,7 @@
#include <linux/vmalloc.h>
#include <linux/set_memory.h>
#include <linux/kfence.h>
+#include <linux/pkeys.h>
#include <asm/barrier.h>
#include <asm/cputype.h>
@@ -1535,3 +1536,42 @@ void __cpu_replace_ttbr1(pgd_t *pgdp, bool cnp)
cpu_uninstall_idmap();
}
+
+#ifdef CONFIG_ARCH_HAS_PKEYS
+int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long init_val)
+{
+ u64 new_por = POE_RXW;
+ u64 old_por;
+ u64 pkey_shift;
+
+ if (!arch_pkeys_enabled())
+ return -ENOSPC;
+
+ /*
+ * This code should only be called with valid 'pkey'
+ * values originating from in-kernel users. Complain
+ * if a bad value is observed.
+ */
+ if (WARN_ON_ONCE(pkey >= arch_max_pkey()))
+ return -EINVAL;
+
+ /* Set the bits we need in POR: */
+ if (init_val & PKEY_DISABLE_ACCESS)
+ new_por = POE_X;
+ else if (init_val & PKEY_DISABLE_WRITE)
+ new_por = POE_RX;
+
+ /* Shift the bits in to the correct place in POR for pkey: */
+ pkey_shift = pkey * POR_BITS_PER_PKEY;
+ new_por <<= pkey_shift;
+
+ /* Get old POR and mask off any old bits in place: */
+ old_por = read_sysreg_s(SYS_POR_EL0);
+ old_por &= ~(POE_MASK << pkey_shift);
+
+ /* Write old part along with new part: */
+ write_sysreg_s(old_por | new_por, SYS_POR_EL0);
+
+ return 0;
+}
+#endif
--
2.25.1
More information about the linux-arm-kernel
mailing list