[PATCH v10 01/10] powerpc/mm: Implement set_memory() routines
Jordan Niethe
jniethe5 at gmail.com
Wed Apr 21 12:51:18 AEST 2021
On Tue, Mar 30, 2021 at 4:16 PM Christophe Leroy
<christophe.leroy at csgroup.eu> wrote:
>
>
>
> Le 30/03/2021 à 06:51, Jordan Niethe a écrit :
> > From: Russell Currey <ruscur at russell.cc>
> >
> > The set_memory_{ro/rw/nx/x}() functions are required for STRICT_MODULE_RWX,
> > and are generally useful primitives to have. This implementation is
> > designed to be completely generic across powerpc's many MMUs.
> >
> > It's possible that this could be optimised to be faster for specific
> > MMUs, but the focus is on having a generic and safe implementation for
> > now.
> >
> > This implementation does not handle cases where the caller is attempting
> > to change the mapping of the page it is executing from, or if another
> > CPU is concurrently using the page being altered. These cases likely
> > shouldn't happen, but a more complex implementation with MMU-specific code
> > could safely handle them, so that is left as a TODO for now.
> >
> > On hash the linear mapping is not kept in the linux pagetable, so this
> > will not change the protection if used on that range. Currently these
> > functions are not used on the linear map so just WARN for now.
> >
> > These functions do nothing if STRICT_KERNEL_RWX is not enabled.
> >
> > Reviewed-by: Daniel Axtens <dja at axtens.net>
> > Signed-off-by: Russell Currey <ruscur at russell.cc>
> > Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
> > [jpn: -rebase on next plus "powerpc/mm/64s: Allow STRICT_KERNEL_RWX again"
> > - WARN on hash linear map]
> > Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
> > ---
> > v10: WARN if trying to change the hash linear map
> > ---
> > arch/powerpc/Kconfig | 1 +
> > arch/powerpc/include/asm/set_memory.h | 32 ++++++++++
> > arch/powerpc/mm/Makefile | 2 +-
> > arch/powerpc/mm/pageattr.c | 88 +++++++++++++++++++++++++++
> > 4 files changed, 122 insertions(+), 1 deletion(-)
> > create mode 100644 arch/powerpc/include/asm/set_memory.h
> > create mode 100644 arch/powerpc/mm/pageattr.c
> >
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index fc7f5c5933e6..4498a27ac9db 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -135,6 +135,7 @@ config PPC
> > select ARCH_HAS_MEMBARRIER_CALLBACKS
> > select ARCH_HAS_MEMBARRIER_SYNC_CORE
> > select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
> > + select ARCH_HAS_SET_MEMORY
> > select ARCH_HAS_STRICT_KERNEL_RWX if ((PPC_BOOK3S_64 || PPC32) && !HIBERNATION)
> > select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> > select ARCH_HAS_UACCESS_FLUSHCACHE
> > diff --git a/arch/powerpc/include/asm/set_memory.h b/arch/powerpc/include/asm/set_memory.h
> > new file mode 100644
> > index 000000000000..64011ea444b4
> > --- /dev/null
> > +++ b/arch/powerpc/include/asm/set_memory.h
> > @@ -0,0 +1,32 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _ASM_POWERPC_SET_MEMORY_H
> > +#define _ASM_POWERPC_SET_MEMORY_H
> > +
> > +#define SET_MEMORY_RO 0
> > +#define SET_MEMORY_RW 1
> > +#define SET_MEMORY_NX 2
> > +#define SET_MEMORY_X 3
> > +
> > +int change_memory_attr(unsigned long addr, int numpages, long action);
> > +
> > +static inline int set_memory_ro(unsigned long addr, int numpages)
> > +{
> > + return change_memory_attr(addr, numpages, SET_MEMORY_RO);
> > +}
> > +
> > +static inline int set_memory_rw(unsigned long addr, int numpages)
> > +{
> > + return change_memory_attr(addr, numpages, SET_MEMORY_RW);
> > +}
> > +
> > +static inline int set_memory_nx(unsigned long addr, int numpages)
> > +{
> > + return change_memory_attr(addr, numpages, SET_MEMORY_NX);
> > +}
> > +
> > +static inline int set_memory_x(unsigned long addr, int numpages)
> > +{
> > + return change_memory_attr(addr, numpages, SET_MEMORY_X);
> > +}
> > +
> > +#endif
> > diff --git a/arch/powerpc/mm/Makefile b/arch/powerpc/mm/Makefile
> > index 3b4e9e4e25ea..d8a08abde1ae 100644
> > --- a/arch/powerpc/mm/Makefile
> > +++ b/arch/powerpc/mm/Makefile
> > @@ -5,7 +5,7 @@
> >
> > ccflags-$(CONFIG_PPC64) := $(NO_MINIMAL_TOC)
> >
> > -obj-y := fault.o mem.o pgtable.o mmap.o maccess.o \
> > +obj-y := fault.o mem.o pgtable.o mmap.o maccess.o pageattr.o \
> > init_$(BITS).o pgtable_$(BITS).o \
> > pgtable-frag.o ioremap.o ioremap_$(BITS).o \
> > init-common.o mmu_context.o drmem.o
> > diff --git a/arch/powerpc/mm/pageattr.c b/arch/powerpc/mm/pageattr.c
> > new file mode 100644
> > index 000000000000..9efcb01088da
> > --- /dev/null
> > +++ b/arch/powerpc/mm/pageattr.c
> > @@ -0,0 +1,88 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/*
> > + * MMU-generic set_memory implementation for powerpc
> > + *
> > + * Copyright 2019, IBM Corporation.
> > + */
> > +
> > +#include <linux/mm.h>
> > +#include <linux/set_memory.h>
> > +
> > +#include <asm/mmu.h>
> > +#include <asm/page.h>
> > +#include <asm/pgtable.h>
> > +
> > +
> > +/*
> > + * Updates the attributes of a page in three steps:
> > + *
> > + * 1. invalidate the page table entry
> > + * 2. flush the TLB
> > + * 3. install the new entry with the updated attributes
> > + *
> > + * This is unsafe if the caller is attempting to change the mapping of the
> > + * page it is executing from, or if another CPU is concurrently using the
> > + * page being altered.
> > + *
> > + * TODO make the implementation resistant to this.
> > + *
> > + * NOTE: can be dangerous to call without STRICT_KERNEL_RWX
> > + */
> > +static int change_page_attr(pte_t *ptep, unsigned long addr, void *data)
> > +{
> > + long action = (long)data;
> > + pte_t pte;
> > +
> > + spin_lock(&init_mm.page_table_lock);
> > +
> > + /* invalidate the PTE so it's safe to modify */
> > + pte = ptep_get_and_clear(&init_mm, addr, ptep);
> > + flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> > +
> > + /* modify the PTE bits as desired, then apply */
> > + switch (action) {
> > + case SET_MEMORY_RO:
> > + pte = pte_wrprotect(pte);
> > + break;
> > + case SET_MEMORY_RW:
> > + pte = pte_mkwrite(pte);
> > + break;
> > + case SET_MEMORY_NX:
> > + pte = pte_exprotect(pte);
> > + break;
> > + case SET_MEMORY_X:
> > + pte = pte_mkexec(pte);
> > + break;
> > + default:
> > + WARN_ON_ONCE(1);
> > + break;
> > + }
> > +
> > + set_pte_at(&init_mm, addr, ptep, pte);
> > + spin_unlock(&init_mm.page_table_lock);
> > +
> > + return 0;
> > +}
> > +
> > +int change_memory_attr(unsigned long addr, int numpages, long action)
> > +{
> > + unsigned long start = ALIGN_DOWN(addr, PAGE_SIZE);
> > + unsigned long sz = numpages * PAGE_SIZE;
> > +
> > + if (!IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
> > + return 0;
>
> You should do this in the header file in order to get it optimised out completely when
> CONFIG_STRICT_KERNEL_RWX is not set.
>
> In asm/set_memory.h you could have:
>
> #ifdef CONFIG_STRICT_KERNEL_RWX
> int change_memory_attr(unsigned long addr, int numpages, long action);
> #else
> static inline int change_memory_attr(unsigned long addr, int numpages, long action) { return 0; }
> #endif
>
> Or another solution is to only define ARCH_HAS_SET_MEMORY when CONFIG_STRICT_KERNEL_RWX is selected.
I think making ARCH_HAS_SET_MEMORY depend on CONFIG_STRICT_KERNEL_RWX
is the way to go.
>
> > +
> > + if (numpages <= 0)
> > + return 0;
> > +
> > +#ifdef CONFIG_PPC_BOOK3S_64
> > + if (WARN_ON_ONCE(!radix_enabled() &&
> > + get_region_id(addr) == LINEAR_MAP_REGION_ID)) {
> > + return -1;
> > + }
> > +#endif
> > +
> > + return apply_to_existing_page_range(&init_mm, start, sz,
> > + change_page_attr, (void *)action);
> > +}
> >
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