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Thu, 07 May 2020 10:28:43 -0700 (PDT) X-Gm-Message-State: AGi0PubeUlfE+OkOQYWmPix7GaE4BiE+iUvMJYzyvMf5z+tBPi8PbW8C nwohxXHohutNlMjb9EuEnkv5ABS11APR4L5EP2k= X-Google-Smtp-Source: APiQypJeZUYOswDUzcXGJeyxztZyS3yyqdhCg00rBZ3EjQpLSNhTrYQ5PFQtOtE5S0FuYnmL7exOZ9afLp5K2EyDFU0= X-Received: by 2002:a92:aa0f:: with SMTP id j15mr16045724ili.211.1588872522480; Thu, 07 May 2020 10:28:42 -0700 (PDT) MIME-Version: 1.0 References: <20200507124522.171323-1-linus.walleij@linaro.org> <20200507124522.171323-4-linus.walleij@linaro.org> In-Reply-To: <20200507124522.171323-4-linus.walleij@linaro.org> From: Ard Biesheuvel Date: Thu, 7 May 2020 19:28:31 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 3/5 v8] ARM: Define the virtual space of KASan's shadow region To: Linus Walleij X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200507_102843_859972_C1F49D79 X-CRM114-Status: GOOD ( 43.99 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Florian Fainelli , Arnd Bergmann , Ard Biesheuvel , Abbott Liu , Russell King , kasan-dev , Alexander Potapenko , Dmitry Vyukov , Andrey Ryabinin , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 7 May 2020 at 14:47, Linus Walleij wrote: > > From: Abbott Liu > > Define KASAN_SHADOW_OFFSET,KASAN_SHADOW_START and KASAN_SHADOW_END for > the Arm kernel address sanitizer. We are "stealing" lowmem (the 4GB > addressable by a 32bit architecture) out of the virtual address > space to use as shadow memory for KASan as follows: > > +----+ 0xffffffff > | |\ > | | |-> Static kernel image (vmlinux) BSS and page table > | |/ > +----+ PAGE_OFFSET > | |\ > | | |-> Loadable kernel modules virtual address space area > | |/ > +----+ MODULES_VADDR = KASAN_SHADOW_END > | |\ > | | |-> The shadow area of kernel virtual address. > | |/ > +----+-> TASK_SIZE (start of kernel space) = KASAN_SHADOW_START the > | |\ shadow address of MODULES_VADDR > | | | > | | | > | | |-> The user space area in lowmem. The kernel address > | | | sanitizer do not use this space, nor does it map it. > | | | > | | | > | | | > | | | > | |/ > ------ 0 > > 0 .. TASK_SIZE is the memory that can be used by shared > userspace/kernelspace. It us used for userspace processes and for > passing parameters and memory buffers in system calls etc. We do not > need to shadow this area. > > KASAN_SHADOW_START: > This value begins with the MODULE_VADDR's shadow address. It is the > start of kernel virtual space. Since we have modules to load, we need > to cover also that area with shadow memory so we can find memory > bugs in modules. > > KASAN_SHADOW_END > This value is the 0x100000000's shadow address: the mapping that would > be after the end of the kernel memory at 0xffffffff. It is the end of > kernel address sanitizer shadow area. It is also the start of the > module area. > > KASAN_SHADOW_OFFSET: > This value is used to map an address to the corresponding shadow > address by the following formula: > > shadow_addr = (address >> 3) + KASAN_SHADOW_OFFSET; > > As you would expect, >> 3 is equal to dividing by 8, meaning each > byte in the shadow memory covers 8 bytes of kernel memory, so one > bit shadow memory per byte of kernel memory is used. > > The KASAN_SHADOW_OFFSET is provided in a Kconfig option depending > on the VMSPLIT layout of the system: the kernel and userspace can > split up lowmem in different ways according to needs, so we calculate > the shadow offset depending on this. > > When kasan is enabled, the definition of TASK_SIZE is not an 8-bit > rotated constant, so we need to modify the TASK_SIZE access code in the > *.s file. > > The kernel and modules may use different amounts of memory, > according to the VMSPLIT configuration, which in turn > determines the PAGE_OFFSET. > > We use the following KASAN_SHADOW_OFFSETs depending on how the > virtual memory is split up: > > - 0x1f000000 if we have 1G userspace / 3G kernelspace split: > - The kernel address space is 3G (0xc0000000) > - PAGE_OFFSET is then set to 0x40000000 so the kernel static > image (vmlinux) uses addresses 0x40000000 .. 0xffffffff > - On top of that we have the MODULES_VADDR which under > the worst case (using ARM instructions) is > PAGE_OFFSET - 16M (0x01000000) = 0x3f000000 > so the modules use addresses 0x3f000000 .. 0x3fffffff > - So the addresses 0x3f000000 .. 0xffffffff need to be > covered with shadow memory. That is 0xc1000000 bytes > of memory. > - 1/8 of that is needed for its shadow memory, so > 0x18200000 bytes of shadow memory is needed. We > "steal" that from the remaining lowmem. > - The KASAN_SHADOW_START becomes 0x26e00000, to > KASAN_SHADOW_END at 0x3effffff. > - Now we can calculate the KASAN_SHADOW_OFFSET for any > kernel address as 0x3f000000 needs to map to the first > byte of shadow memory and 0xffffffff needs to map to > the last byte of shadow memory. Since: > SHADOW_ADDR = (address >> 3) + KASAN_SHADOW_OFFSET > 0x26e00000 = (0x3f000000 >> 3) + KASAN_SHADOW_OFFSET > KASAN_SHADOW_OFFSET = 0x26e00000 - (0x3f000000 >> 3) > KASAN_SHADOW_OFFSET = 0x26e00000 - 0x07e00000 > KASAN_SHADOW_OFFSET = 0x1f000000 > > - 0x5f000000 if we have 2G userspace / 2G kernelspace split: > - The kernel space is 2G (0x80000000) > - PAGE_OFFSET is set to 0x80000000 so the kernel static > image uses 0x80000000 .. 0xffffffff. > - On top of that we have the MODULES_VADDR which under > the worst case (using ARM instructions) is > PAGE_OFFSET - 16M (0x01000000) = 0x7f000000 > so the modules use addresses 0x7f000000 .. 0x7fffffff > - So the addresses 0x7f000000 .. 0xffffffff need to be > covered with shadow memory. That is 0x81000000 bytes > of memory. > - 1/8 of that is needed for its shadow memory, so > 0x10200000 bytes of shadow memory is needed. We > "steal" that from the remaining lowmem. > - The KASAN_SHADOW_START becomes 0x6ee00000, to > KASAN_SHADOW_END at 0x7effffff. > - Now we can calculate the KASAN_SHADOW_OFFSET for any > kernel address as 0x7f000000 needs to map to the first > byte of shadow memory and 0xffffffff needs to map to > the last byte of shadow memory. Since: > SHADOW_ADDR = (address >> 3) + KASAN_SHADOW_OFFSET > 0x6ee00000 = (0x7f000000 >> 3) + KASAN_SHADOW_OFFSET > KASAN_SHADOW_OFFSET = 0x6ee00000 - (0x7f000000 >> 3) > KASAN_SHADOW_OFFSET = 0x6ee00000 - 0x0fe00000 > KASAN_SHADOW_OFFSET = 0x5f000000 > > - 0x9f000000 if we have 3G userspace / 1G kernelspace split, > and this is the default split for ARM: > - The kernel address space is 1GB (0x40000000) > - PAGE_OFFSET is set to 0xc0000000 so the kernel static > image uses 0xc0000000 .. 0xffffffff. > - On top of that we have the MODULES_VADDR which under > the worst case (using ARM instructions) is > PAGE_OFFSET - 16M (0x01000000) = 0xbf000000 > so the modules use addresses 0xbf000000 .. 0xbfffffff > - So the addresses 0xbf000000 .. 0xffffffff need to be > covered with shadow memory. That is 0x41000000 bytes > of memory. > - 1/8 of that is needed for its shadow memory, so > 0x08200000 bytes of shadow memory is needed. We > "steal" that from the remaining lowmem. > - The KASAN_SHADOW_START becomes 0xb6e00000, to > KASAN_SHADOW_END at 0xbfffffff. > - Now we can calculate the KASAN_SHADOW_OFFSET for any > kernel address as 0xbf000000 needs to map to the first > byte of shadow memory and 0xffffffff needs to map to > the last byte of shadow memory. Since: > SHADOW_ADDR = (address >> 3) + KASAN_SHADOW_OFFSET > 0xb6e00000 = (0xbf000000 >> 3) + KASAN_SHADOW_OFFSET > KASAN_SHADOW_OFFSET = 0xb6e00000 - (0xbf000000 >> 3) > KASAN_SHADOW_OFFSET = 0xb6e00000 - 0x17e00000 > KASAN_SHADOW_OFFSET = 0x9f000000 > > - 0x8f000000 if we have 3G userspace / 1G kernelspace with > full 1 GB low memory (VMSPLIT_3G_OPT): > - The kernel address space is 1GB (0x40000000) > - PAGE_OFFSET is set to 0xb0000000 so the kernel static > image uses 0xb0000000 .. 0xffffffff. > - On top of that we have the MODULES_VADDR which under > the worst case (using ARM instructions) is > PAGE_OFFSET - 16M (0x01000000) = 0xaf000000 > so the modules use addresses 0xaf000000 .. 0xaffffff > - So the addresses 0xaf000000 .. 0xffffffff need to be > covered with shadow memory. That is 0x51000000 bytes > of memory. > - 1/8 of that is needed for its shadow memory, so > 0x0a200000 bytes of shadow memory is needed. We > "steal" that from the remaining lowmem. > - The KASAN_SHADOW_START becomes 0xa4e00000, to > KASAN_SHADOW_END at 0xaeffffff. > - Now we can calculate the KASAN_SHADOW_OFFSET for any > kernel address as 0xaf000000 needs to map to the first > byte of shadow memory and 0xffffffff needs to map to > the last byte of shadow memory. Since: > SHADOW_ADDR = (address >> 3) + KASAN_SHADOW_OFFSET > 0xa4e00000 = (0xaf000000 >> 3) + KASAN_SHADOW_OFFSET > KASAN_SHADOW_OFFSET = 0xa4e00000 - (0xaf000000 >> 3) > KASAN_SHADOW_OFFSET = 0xa4e00000 - 0x15e00000 > KASAN_SHADOW_OFFSET = 0x8f000000 > > - The default value of 0xffffffff for KASAN_SHADOW_OFFSET > is an error value. We should always match one of the > above shadow offsets. > > When we do this, TASK_SIZE will sometimes get a bit odd values > that will not fit into immediate mov assembly instructions. > To account for this, we need to rewrite some assembly using > TASK_SIZE like this: > > - mov r1, #TASK_SIZE > + ldr r1, =TASK_SIZE > > or > > - cmp r4, #TASK_SIZE > + ldr r0, =TASK_SIZE > + cmp r4, r0 > > this is done to avoid the immediate #TASK_SIZE that need to > fit into a limited number of bits. > It would be good to note that the assembler will actually turn this into a mov instruction if the immediate fits, so these LDRs will only be true loads in the CONFIG_KASAN=y case. > Cc: Andrey Ryabinin > Cc: Alexander Potapenko > Cc: Dmitry Vyukov > Cc: kasan-dev@googlegroups.com > Reported-by: Ard Biesheuvel > Signed-off-by: Abbott Liu > Signed-off-by: Florian Fainelli > Signed-off-by: Linus Walleij > --- > ChangeLog v7->v8: > - Rewrote the PMD clearing code to take into account that > KASan may not always be adjacent to MODULES_VADDR: if we > compile for thumb, then there will be an 8 MB hole between > the shadow memory and MODULES_VADDR. Make this explicit and > use the KASAN defines with an explicit ifdef so it is clear > what is going on in the prepare_page_table(). > - Patch memory.rst to reflect the location of KASan shadow > memory. > ChangeLog v6->v7: > - Use the SPDX license identifier. > - Rewrote the commit message and updates the illustration. > - Move KASAN_OFFSET Kconfig set-up into this patch and put it > right after PAGE_OFFSET so it is clear how this works, and > we have all defines in one patch. > - Added KASAN_SHADOW_OFFSET of 0x8f000000 for 3G_OPT. > See the calculation in the commit message. > - Updated the commit message with detailed information on > how KASAN_SHADOW_OFFSET is obtained for the different > VMSPLIT/PAGE_OFFSET options. > --- > Documentation/arm/memory.rst | 5 ++ > arch/arm/Kconfig | 9 ++++ > arch/arm/include/asm/kasan_def.h | 81 ++++++++++++++++++++++++++++++++ > arch/arm/include/asm/memory.h | 5 ++ > arch/arm/kernel/entry-armv.S | 5 +- > arch/arm/kernel/entry-common.S | 9 ++-- > arch/arm/mm/mmu.c | 18 +++++++ > 7 files changed, 127 insertions(+), 5 deletions(-) > create mode 100644 arch/arm/include/asm/kasan_def.h > > diff --git a/Documentation/arm/memory.rst b/Documentation/arm/memory.rst > index 0521b4ce5c96..36bae90cfb1e 100644 > --- a/Documentation/arm/memory.rst > +++ b/Documentation/arm/memory.rst > @@ -72,6 +72,11 @@ MODULES_VADDR MODULES_END-1 Kernel module space > Kernel modules inserted via insmod are > placed here using dynamic mappings. > > +TASK_SIZE MODULES_VADDR-1 KASAn shadow memory when KASan is in use. > + The range from MODULES_VADDR to the top > + of the memory is shadowed here with 1 bit > + per byte of memory. > + > 00001000 TASK_SIZE-1 User space mappings > Per-thread mappings are placed here via > the mmap() system call. > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index 66a04f6f4775..f6f2d3b202f5 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -1325,6 +1325,15 @@ config PAGE_OFFSET > default 0xB0000000 if VMSPLIT_3G_OPT > default 0xC0000000 > > +config KASAN_SHADOW_OFFSET > + hex > + depends on KASAN > + default 0x1f000000 if PAGE_OFFSET=0x40000000 > + default 0x5f000000 if PAGE_OFFSET=0x80000000 > + default 0x9f000000 if PAGE_OFFSET=0xC0000000 > + default 0x8f000000 if PAGE_OFFSET=0xB0000000 > + default 0xffffffff > + > config NR_CPUS > int "Maximum number of CPUs (2-32)" > range 2 32 > diff --git a/arch/arm/include/asm/kasan_def.h b/arch/arm/include/asm/kasan_def.h > new file mode 100644 > index 000000000000..5739605aa7cf > --- /dev/null > +++ b/arch/arm/include/asm/kasan_def.h > @@ -0,0 +1,81 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * arch/arm/include/asm/kasan_def.h > + * > + * Copyright (c) 2018 Huawei Technologies Co., Ltd. > + * > + * Author: Abbott Liu > + */ > + > +#ifndef __ASM_KASAN_DEF_H > +#define __ASM_KASAN_DEF_H > + > +#ifdef CONFIG_KASAN > + > +/* > + * Define KASAN_SHADOW_OFFSET,KASAN_SHADOW_START and KASAN_SHADOW_END for > + * the Arm kernel address sanitizer. We are "stealing" lowmem (the 4GB > + * addressable by a 32bit architecture) out of the virtual address > + * space to use as shadow memory for KASan as follows: > + * > + * +----+ 0xffffffff > + * | | \ > + * | | |-> Static kernel image (vmlinux) BSS and page table > + * | |/ > + * +----+ PAGE_OFFSET > + * | | \ > + * | | |-> Loadable kernel modules virtual address space area > + * | |/ > + * +----+ MODULES_VADDR = KASAN_SHADOW_END > + * | | \ > + * | | |-> The shadow area of kernel virtual address. > + * | |/ > + * +----+-> TASK_SIZE (start of kernel space) = KASAN_SHADOW_START the > + * | |\ shadow address of MODULES_VADDR > + * | | | > + * | | | > + * | | |-> The user space area in lowmem. The kernel address > + * | | | sanitizer do not use this space, nor does it map it. > + * | | | > + * | | | > + * | | | > + * | | | > + * | |/ > + * ------ 0 > + * > + * 1) KASAN_SHADOW_START > + * This value begins with the MODULE_VADDR's shadow address. It is the > + * start of kernel virtual space. Since we have modules to load, we need > + * to cover also that area with shadow memory so we can find memory > + * bugs in modules. > + * > + * 2) KASAN_SHADOW_END > + * This value is the 0x100000000's shadow address: the mapping that would > + * be after the end of the kernel memory at 0xffffffff. It is the end of > + * kernel address sanitizer shadow area. It is also the start of the > + * module area. > + * > + * 3) KASAN_SHADOW_OFFSET: > + * This value is used to map an address to the corresponding shadow > + * address by the following formula: > + * > + * shadow_addr = (address >> 3) + KASAN_SHADOW_OFFSET; > + * > + * As you would expect, >> 3 is equal to dividing by 8, meaning each > + * byte in the shadow memory covers 8 bytes of kernel memory, so one > + * bit shadow memory per byte of kernel memory is used. > + * > + * The KASAN_SHADOW_OFFSET is provided in a Kconfig option depending > + * on the VMSPLIT layout of the system: the kernel and userspace can > + * split up lowmem in different ways according to needs, so we calculate > + * the shadow offset depending on this. > + */ > + > +#define KASAN_SHADOW_SCALE_SHIFT 3 > +#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL) > +#define KASAN_SHADOW_END ((UL(1) << (32 - KASAN_SHADOW_SCALE_SHIFT)) \ > + + KASAN_SHADOW_OFFSET) > +#define KASAN_SHADOW_START ((KASAN_SHADOW_END >> 3) + KASAN_SHADOW_OFFSET) > + > +#endif > +#endif > diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h > index 99035b5891ef..5cfa9e5dc733 100644 > --- a/arch/arm/include/asm/memory.h > +++ b/arch/arm/include/asm/memory.h > @@ -18,6 +18,7 @@ > #ifdef CONFIG_NEED_MACH_MEMORY_H > #include > #endif > +#include > > /* PAGE_OFFSET - the virtual address of the start of the kernel image */ > #define PAGE_OFFSET UL(CONFIG_PAGE_OFFSET) > @@ -28,7 +29,11 @@ > * TASK_SIZE - the maximum size of a user space task. > * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area > */ > +#ifndef CONFIG_KASAN > #define TASK_SIZE (UL(CONFIG_PAGE_OFFSET) - UL(SZ_16M)) > +#else > +#define TASK_SIZE (KASAN_SHADOW_START) > +#endif > #define TASK_UNMAPPED_BASE ALIGN(TASK_SIZE / 3, SZ_16M) > > /* > diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S > index 77f54830554c..7548d38599ae 100644 > --- a/arch/arm/kernel/entry-armv.S > +++ b/arch/arm/kernel/entry-armv.S > @@ -180,7 +180,7 @@ ENDPROC(__und_invalid) > > get_thread_info tsk > ldr r0, [tsk, #TI_ADDR_LIMIT] > - mov r1, #TASK_SIZE > + ldr r1, =TASK_SIZE > str r1, [tsk, #TI_ADDR_LIMIT] > str r0, [sp, #SVC_ADDR_LIMIT] > > @@ -434,7 +434,8 @@ ENDPROC(__fiq_abt) > @ if it was interrupted in a critical region. Here we > @ perform a quick test inline since it should be false > @ 99.9999% of the time. The rest is done out of line. > - cmp r4, #TASK_SIZE > + ldr r0, =TASK_SIZE > + cmp r4, r0 > blhs kuser_cmpxchg64_fixup > #endif > #endif > diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S > index 271cb8a1eba1..fee279e28a72 100644 > --- a/arch/arm/kernel/entry-common.S > +++ b/arch/arm/kernel/entry-common.S > @@ -50,7 +50,8 @@ __ret_fast_syscall: > UNWIND(.cantunwind ) > disable_irq_notrace @ disable interrupts > ldr r2, [tsk, #TI_ADDR_LIMIT] > - cmp r2, #TASK_SIZE > + ldr r1, =TASK_SIZE > + cmp r2, r1 > blne addr_limit_check_failed > ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing > tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK > @@ -87,7 +88,8 @@ __ret_fast_syscall: > #endif > disable_irq_notrace @ disable interrupts > ldr r2, [tsk, #TI_ADDR_LIMIT] > - cmp r2, #TASK_SIZE > + ldr r1, =TASK_SIZE > + cmp r2, r1 > blne addr_limit_check_failed > ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing > tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK > @@ -128,7 +130,8 @@ ret_slow_syscall: > disable_irq_notrace @ disable interrupts > ENTRY(ret_to_user_from_irq) > ldr r2, [tsk, #TI_ADDR_LIMIT] > - cmp r2, #TASK_SIZE > + ldr r1, =TASK_SIZE > + cmp r2, r1 > blne addr_limit_check_failed > ldr r1, [tsk, #TI_FLAGS] > tst r1, #_TIF_WORK_MASK > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c > index ec8d0008bfa1..092bebd9ffc2 100644 > --- a/arch/arm/mm/mmu.c > +++ b/arch/arm/mm/mmu.c > @@ -29,6 +29,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -1246,8 +1247,25 @@ static inline void prepare_page_table(void) > /* > * Clear out all the mappings below the kernel image. > */ > +#ifdef CONFIG_KASAN > + /* > + * KASan's shadow memory inserts itself between the TASK_SIZE > + * and MODULES_VADDR. Do not clear the KASan shadow memory mappings. > + */ > + for (addr = 0; addr < KASAN_SHADOW_START; addr += PMD_SIZE) > + pmd_clear(pmd_off_k(addr)); > + /* > + * Skip over the KASan shadow area. KASAN_SHADOW_END is sometimes > + * equal to MODULES_VADDR and then we exit the pmd clearing. If we > + * are using a thumb-compiled kernel, there there will be 8MB more > + * to clear as KASan always offset to 16 MB below MODULES_VADDR. > + */ > + for (addr = KASAN_SHADOW_END; addr < MODULES_VADDR; addr += PMD_SIZE) > + pmd_clear(pmd_off_k(addr)); > +#else > for (addr = 0; addr < MODULES_VADDR; addr += PMD_SIZE) > pmd_clear(pmd_off_k(addr)); > +#endif > > #ifdef CONFIG_XIP_KERNEL > /* The XIP kernel is mapped in the module area -- skip over it */ > -- > 2.25.4 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel