[PATCH v4 17/29] arm64: implement PKEYS support
Joey Gouly
joey.gouly at arm.com
Tue May 28 21:26:19 AEST 2024
Hi Amit,
Thanks for taking a look!
On Tue, May 28, 2024 at 12:25:58PM +0530, Amit Daniel Kachhap wrote:
>
>
> On 5/3/24 18:31, Joey Gouly wrote:
> > 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;
>
> The above check can be dropped as the caller of this function
> fault_from_pkey() does the same check.
arch_vma_access_permitted() is called by other places in the kernel, so I need to leave that check in.
Thanks,
Joey
>
> Thanks,
> Amit
>
> > +
> > + /* 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
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