From: Russell Currey <ruscur@russell.cc> To: Christophe Leroy <christophe.leroy@c-s.fr>, linuxppc-dev@lists.ozlabs.org Cc: ajd@linux.ibm.com, kernel-hardening@lists.openwall.com, npiggin@gmail.com, joel@jms.id.au, dja@axtens.net Subject: Re: [PATCH v6 1/5] powerpc/mm: Implement set_memory() routines Date: Mon, 03 Feb 2020 11:46:37 +1100 [thread overview] Message-ID: <8675c11631ac027a78e00d4fe2c20736496b1e97.camel@russell.cc> (raw) In-Reply-To: <8f8940e2-c6ab-fca2-ab8a-61b80b2edd22@c-s.fr> On Wed, 2020-01-08 at 13:52 +0100, Christophe Leroy wrote: > > Le 24/12/2019 à 06:55, Russell Currey a écrit : > > 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. > > > > Signed-off-by: Russell Currey <ruscur@russell.cc> > > --- > > arch/powerpc/Kconfig | 1 + > > arch/powerpc/include/asm/set_memory.h | 32 +++++++++++ > > arch/powerpc/mm/Makefile | 1 + > > arch/powerpc/mm/pageattr.c | 83 > > +++++++++++++++++++++++++++ > > 4 files changed, 117 insertions(+) > > 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 1ec34e16ed65..f0b9b47b5353 100644 > > --- a/arch/powerpc/Kconfig > > +++ b/arch/powerpc/Kconfig > > @@ -133,6 +133,7 @@ config PPC > > select ARCH_HAS_PTE_SPECIAL > > select ARCH_HAS_MEMBARRIER_CALLBACKS > > 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) && !RELOCATABLE && !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..5230ddb2fefd > > --- /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 1 > > +#define SET_MEMORY_RW 2 > > +#define SET_MEMORY_NX 3 > > +#define SET_MEMORY_X 4 > > Maybe going from 0 to 3 would be better than 1 to 4 > > > + > > +int change_memory_attr(unsigned long addr, int numpages, int > > action); > > action could be unsigned. > > > + > > +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 5e147986400d..d0a0bcbc9289 100644 > > --- a/arch/powerpc/mm/Makefile > > +++ b/arch/powerpc/mm/Makefile > > @@ -20,3 +20,4 @@ obj-$(CONFIG_HIGHMEM) += highmem.o > > obj-$(CONFIG_PPC_COPRO_BASE) += copro_fault.o > > obj-$(CONFIG_PPC_PTDUMP) += ptdump/ > > obj-$(CONFIG_KASAN) += kasan/ > > +obj-$(CONFIG_ARCH_HAS_SET_MEMORY) += pageattr.o > > CONFIG_ARCH_HAS_SET_MEMORY is set inconditionnally, I think you > should > add pageattr.o to obj-y instead. CONFIG_ARCH_HAS_XXX are almost > never > used in Makefiles Fair enough, will keep that in mind > > > diff --git a/arch/powerpc/mm/pageattr.c > > b/arch/powerpc/mm/pageattr.c > > new file mode 100644 > > index 000000000000..15d5fb04f531 > > --- /dev/null > > +++ b/arch/powerpc/mm/pageattr.c > > @@ -0,0 +1,83 @@ > > +// 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. > > + */ > > +static int __change_page_attr(pte_t *ptep, unsigned long addr, > > void *data) > > +{ > > + int action = *((int *)data); > > Don't use pointers for so simple things, pointers forces the compiler > to > setup a stack frame and save the data into stack. Instead do: > > int action = (int)data; > > > + pte_t pte_val; > > + > > + // invalidate the PTE so it's safe to modify > > + pte_val = ptep_get_and_clear(&init_mm, addr, ptep); > > + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); > > Why flush a range for a single page ? On most targets this will do a > tlbia which is heavy, while a tlbie would suffice. > > I think flush_tlb_kernel_range() should be replaced by something > flushing only a single page. You might be able to help me out here, I wanted to do that but the only functions I could find that flushed single pages needed a vm_area_struct, which I can't get. > > > + > > + // modify the PTE bits as desired, then apply > > + switch (action) { > > + case SET_MEMORY_RO: > > + pte_val = pte_wrprotect(pte_val); > > + break; > > + case SET_MEMORY_RW: > > + pte_val = pte_mkwrite(pte_val); > > + break; > > + case SET_MEMORY_NX: > > + pte_val = pte_exprotect(pte_val); > > + break; > > + case SET_MEMORY_X: > > + pte_val = pte_mkexec(pte_val); > > + break; > > + default: > > + WARN_ON(true); > > + return -EINVAL; > > Is it worth checking that the action is valid for each page ? I > think > validity of action should be checked in change_memory_attr(). All > other > functions are static so you know they won't be called from outside. > > Once done, you can squash __change_page_attr() into > change_page_attr(), > remove the ret var and return 0 all the time. Makes sense to fold things into a single function, but in terms of performance it shouldn't make a difference, right? I still have to check the action to determine what to change (unless I replace passing SET_MEMORY_RO into apply_to_page_range() with a function pointer to pte_wrprotect() for example). > > > + } > > + > > + set_pte_at(&init_mm, addr, ptep, pte_val); > > + > > + return 0; > > +} > > + > > +static int change_page_attr(pte_t *ptep, unsigned long addr, void > > *data) > > +{ > > + int ret; > > + > > + spin_lock(&init_mm.page_table_lock); > > + ret = __change_page_attr(ptep, addr, data); > > + spin_unlock(&init_mm.page_table_lock); > > + > > + return ret; > > +} > > + > > +int change_memory_attr(unsigned long addr, int numpages, int > > action) > > +{ > > + unsigned long start = ALIGN_DOWN(addr, PAGE_SIZE); > > + unsigned long size = numpages * PAGE_SIZE; > > + > > + if (!numpages) > > + return 0; > > + > > + return apply_to_page_range(&init_mm, start, size, > > change_page_attr, &action); > > Use (void*)action instead of &action (see upper comment) To get this to work I had to use (void *)(size_t)action to stop the compiler from complaining about casting an int to a void*, is there a better way to go about it? Works fine, just looks gross. > > > +} > > > > Christophe >
WARNING: multiple messages have this Message-ID (diff)
From: Russell Currey <ruscur@russell.cc> To: Christophe Leroy <christophe.leroy@c-s.fr>, linuxppc-dev@lists.ozlabs.org Cc: joel@jms.id.au, mpe@ellerman.id.au, ajd@linux.ibm.com, dja@axtens.net, npiggin@gmail.com, kernel-hardening@lists.openwall.com Subject: Re: [PATCH v6 1/5] powerpc/mm: Implement set_memory() routines Date: Mon, 03 Feb 2020 11:46:37 +1100 [thread overview] Message-ID: <8675c11631ac027a78e00d4fe2c20736496b1e97.camel@russell.cc> (raw) In-Reply-To: <8f8940e2-c6ab-fca2-ab8a-61b80b2edd22@c-s.fr> On Wed, 2020-01-08 at 13:52 +0100, Christophe Leroy wrote: > > Le 24/12/2019 à 06:55, Russell Currey a écrit : > > 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. > > > > Signed-off-by: Russell Currey <ruscur@russell.cc> > > --- > > arch/powerpc/Kconfig | 1 + > > arch/powerpc/include/asm/set_memory.h | 32 +++++++++++ > > arch/powerpc/mm/Makefile | 1 + > > arch/powerpc/mm/pageattr.c | 83 > > +++++++++++++++++++++++++++ > > 4 files changed, 117 insertions(+) > > 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 1ec34e16ed65..f0b9b47b5353 100644 > > --- a/arch/powerpc/Kconfig > > +++ b/arch/powerpc/Kconfig > > @@ -133,6 +133,7 @@ config PPC > > select ARCH_HAS_PTE_SPECIAL > > select ARCH_HAS_MEMBARRIER_CALLBACKS > > 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) && !RELOCATABLE && !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..5230ddb2fefd > > --- /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 1 > > +#define SET_MEMORY_RW 2 > > +#define SET_MEMORY_NX 3 > > +#define SET_MEMORY_X 4 > > Maybe going from 0 to 3 would be better than 1 to 4 > > > + > > +int change_memory_attr(unsigned long addr, int numpages, int > > action); > > action could be unsigned. > > > + > > +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 5e147986400d..d0a0bcbc9289 100644 > > --- a/arch/powerpc/mm/Makefile > > +++ b/arch/powerpc/mm/Makefile > > @@ -20,3 +20,4 @@ obj-$(CONFIG_HIGHMEM) += highmem.o > > obj-$(CONFIG_PPC_COPRO_BASE) += copro_fault.o > > obj-$(CONFIG_PPC_PTDUMP) += ptdump/ > > obj-$(CONFIG_KASAN) += kasan/ > > +obj-$(CONFIG_ARCH_HAS_SET_MEMORY) += pageattr.o > > CONFIG_ARCH_HAS_SET_MEMORY is set inconditionnally, I think you > should > add pageattr.o to obj-y instead. CONFIG_ARCH_HAS_XXX are almost > never > used in Makefiles Fair enough, will keep that in mind > > > diff --git a/arch/powerpc/mm/pageattr.c > > b/arch/powerpc/mm/pageattr.c > > new file mode 100644 > > index 000000000000..15d5fb04f531 > > --- /dev/null > > +++ b/arch/powerpc/mm/pageattr.c > > @@ -0,0 +1,83 @@ > > +// 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. > > + */ > > +static int __change_page_attr(pte_t *ptep, unsigned long addr, > > void *data) > > +{ > > + int action = *((int *)data); > > Don't use pointers for so simple things, pointers forces the compiler > to > setup a stack frame and save the data into stack. Instead do: > > int action = (int)data; > > > + pte_t pte_val; > > + > > + // invalidate the PTE so it's safe to modify > > + pte_val = ptep_get_and_clear(&init_mm, addr, ptep); > > + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); > > Why flush a range for a single page ? On most targets this will do a > tlbia which is heavy, while a tlbie would suffice. > > I think flush_tlb_kernel_range() should be replaced by something > flushing only a single page. You might be able to help me out here, I wanted to do that but the only functions I could find that flushed single pages needed a vm_area_struct, which I can't get. > > > + > > + // modify the PTE bits as desired, then apply > > + switch (action) { > > + case SET_MEMORY_RO: > > + pte_val = pte_wrprotect(pte_val); > > + break; > > + case SET_MEMORY_RW: > > + pte_val = pte_mkwrite(pte_val); > > + break; > > + case SET_MEMORY_NX: > > + pte_val = pte_exprotect(pte_val); > > + break; > > + case SET_MEMORY_X: > > + pte_val = pte_mkexec(pte_val); > > + break; > > + default: > > + WARN_ON(true); > > + return -EINVAL; > > Is it worth checking that the action is valid for each page ? I > think > validity of action should be checked in change_memory_attr(). All > other > functions are static so you know they won't be called from outside. > > Once done, you can squash __change_page_attr() into > change_page_attr(), > remove the ret var and return 0 all the time. Makes sense to fold things into a single function, but in terms of performance it shouldn't make a difference, right? I still have to check the action to determine what to change (unless I replace passing SET_MEMORY_RO into apply_to_page_range() with a function pointer to pte_wrprotect() for example). > > > + } > > + > > + set_pte_at(&init_mm, addr, ptep, pte_val); > > + > > + return 0; > > +} > > + > > +static int change_page_attr(pte_t *ptep, unsigned long addr, void > > *data) > > +{ > > + int ret; > > + > > + spin_lock(&init_mm.page_table_lock); > > + ret = __change_page_attr(ptep, addr, data); > > + spin_unlock(&init_mm.page_table_lock); > > + > > + return ret; > > +} > > + > > +int change_memory_attr(unsigned long addr, int numpages, int > > action) > > +{ > > + unsigned long start = ALIGN_DOWN(addr, PAGE_SIZE); > > + unsigned long size = numpages * PAGE_SIZE; > > + > > + if (!numpages) > > + return 0; > > + > > + return apply_to_page_range(&init_mm, start, size, > > change_page_attr, &action); > > Use (void*)action instead of &action (see upper comment) To get this to work I had to use (void *)(size_t)action to stop the compiler from complaining about casting an int to a void*, is there a better way to go about it? Works fine, just looks gross. > > > +} > > > > Christophe >
next prev parent reply other threads:[~2020-02-03 0:48 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-12-24 5:55 [PATCH v6 0/5] Implement STRICT_MODULE_RWX for powerpc Russell Currey 2019-12-24 5:55 ` Russell Currey 2019-12-24 5:55 ` [PATCH v6 1/5] powerpc/mm: Implement set_memory() routines Russell Currey 2019-12-24 5:55 ` Russell Currey 2020-01-08 12:52 ` Christophe Leroy 2020-01-08 12:52 ` Christophe Leroy 2020-02-03 0:46 ` Russell Currey [this message] 2020-02-03 0:46 ` Russell Currey 2020-02-03 7:06 ` Christophe Leroy 2020-02-03 7:06 ` Christophe Leroy 2020-01-20 8:35 ` Christophe Leroy 2020-01-20 8:35 ` Christophe Leroy 2019-12-24 5:55 ` [PATCH v6 2/5] powerpc/kprobes: Mark newly allocated probes as RO Russell Currey 2019-12-24 5:55 ` Russell Currey 2020-01-08 16:48 ` Christophe Leroy 2020-01-08 16:48 ` Christophe Leroy 2019-12-24 5:55 ` [PATCH v6 3/5] powerpc/mm/ptdump: debugfs handler for W+X checks at runtime Russell Currey 2019-12-24 5:55 ` Russell Currey 2019-12-31 17:14 ` Christophe Leroy 2019-12-31 17:14 ` Christophe Leroy 2020-01-07 10:48 ` Michael Ellerman 2020-01-07 10:48 ` Michael Ellerman 2019-12-24 5:55 ` [PATCH v6 4/5] powerpc: Set ARCH_HAS_STRICT_MODULE_RWX Russell Currey 2019-12-24 5:55 ` Russell Currey 2019-12-24 5:55 ` [PATCH v6 5/5] powerpc/configs: Enable STRICT_MODULE_RWX in skiroot_defconfig Russell Currey 2019-12-24 5:55 ` Russell Currey
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=8675c11631ac027a78e00d4fe2c20736496b1e97.camel@russell.cc \ --to=ruscur@russell.cc \ --cc=ajd@linux.ibm.com \ --cc=christophe.leroy@c-s.fr \ --cc=dja@axtens.net \ --cc=joel@jms.id.au \ --cc=kernel-hardening@lists.openwall.com \ --cc=linuxppc-dev@lists.ozlabs.org \ --cc=npiggin@gmail.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.