Messages in this thread Patch in this message | | | Date | Tue, 25 Feb 2020 16:46:08 -0800 | Subject | [PATCH] UML: add support for KASAN under x86_64 | From | Patricia Alfonso <> |
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Make KASAN run on User Mode Linux on x86_64.
Depends on Constructor support in UML - "[RFC PATCH] um: implement CONFIG_CONSTRUCTORS for modules" (https://patchwork.ozlabs.org/patch/1234551/) by Johannes Berg.
The location of the KASAN shadow memory, starting at KASAN_SHADOW_OFFSET, can be configured using the KASAN_SHADOW_OFFSET option. UML uses roughly 18TB of address space, and KASAN requires 1/8th of this. The default location of this offset is 0x7fff8000 as suggested by Dmitry Vyukov. There is usually enough free space at this location; however, it is a config option so that it can be easily changed if needed.
The UML-specific KASAN initializer uses mmap to map the roughly 2.25TB of shadow memory to the location defined by KASAN_SHADOW_OFFSET. kasan_init() utilizes constructors to initialize KASAN before main().
Disable stack instrumentation on UML via KASAN_STACK config option to avoid false positive KASAN reports.
Signed-off-by: Patricia Alfonso <trishalfonso@google.com> --- arch/um/Kconfig | 13 +++++++++++++ arch/um/Makefile | 6 ++++++ arch/um/include/asm/common.lds.S | 1 + arch/um/include/asm/kasan.h | 32 ++++++++++++++++++++++++++++++++ arch/um/kernel/dyn.lds.S | 5 ++++- arch/um/kernel/mem.c | 18 ++++++++++++++++++ arch/um/os-Linux/mem.c | 22 ++++++++++++++++++++++ arch/um/os-Linux/user_syms.c | 4 ++-- arch/x86/um/Makefile | 3 ++- arch/x86/um/vdso/Makefile | 3 +++ lib/Kconfig.kasan | 2 +- 11 files changed, 104 insertions(+), 5 deletions(-) create mode 100644 arch/um/include/asm/kasan.h
diff --git a/arch/um/Kconfig b/arch/um/Kconfig index 0917f8443c28..fb2ad1fb05fd 100644 --- a/arch/um/Kconfig +++ b/arch/um/Kconfig @@ -8,6 +8,7 @@ config UML select ARCH_HAS_KCOV select ARCH_NO_PREEMPT select HAVE_ARCH_AUDITSYSCALL + select HAVE_ARCH_KASAN if X86_64 select HAVE_ARCH_SECCOMP_FILTER select HAVE_ASM_MODVERSIONS select HAVE_UID16 @@ -200,6 +201,18 @@ config UML_TIME_TRAVEL_SUPPORT It is safe to say Y, but you probably don't need this. +config KASAN_SHADOW_OFFSET + hex + depends on KASAN + default 0x7fff8000 + help + This is the offset at which the ~2.25TB of shadow memory is + mapped and used by KASAN for memory debugging. This can be any + address that has at least KASAN_SHADOW_SIZE(total address space divided + by 8) amount of space so that the KASAN shadow memory does not conflict + with anything. The default is 0x7fff8000, as it fits into immediate of + most instructions. + endmenu source "arch/um/drivers/Kconfig" diff --git a/arch/um/Makefile b/arch/um/Makefile index d2daa206872d..28fe7a9a1858 100644 --- a/arch/um/Makefile +++ b/arch/um/Makefile @@ -75,6 +75,12 @@ USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \ -D_FILE_OFFSET_BITS=64 -idirafter $(srctree)/include \ -idirafter $(objtree)/include -D__KERNEL__ -D__UM_HOST__ +# Kernel config options are not included in USER_CFLAGS, but the option for KASAN +# should be included if the KASAN config option was set. +ifdef CONFIG_KASAN + USER_CFLAGS+=-DCONFIG_KASAN=y +endif + #This will adjust *FLAGS accordingly to the platform. include $(ARCH_DIR)/Makefile-os-$(OS) diff --git a/arch/um/include/asm/common.lds.S b/arch/um/include/asm/common.lds.S index eca6c452a41b..731f8c8422a2 100644 --- a/arch/um/include/asm/common.lds.S +++ b/arch/um/include/asm/common.lds.S @@ -83,6 +83,7 @@ } .init_array : { __init_array_start = .; + *(.kasan_init) *(.init_array) __init_array_end = .; } diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h new file mode 100644 index 000000000000..2b81e7bcd4af --- /dev/null +++ b/arch/um/include/asm/kasan.h @@ -0,0 +1,32 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __ASM_UM_KASAN_H +#define __ASM_UM_KASAN_H + +#include <linux/init.h> +#include <linux/const.h> + +#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL) + +/* used in kasan_mem_to_shadow to divide by 8 */ +#define KASAN_SHADOW_SCALE_SHIFT 3 + +#ifdef CONFIG_X86_64 +#define KASAN_HOST_USER_SPACE_END_ADDR 0x00007fffffffffffUL +/* KASAN_SHADOW_SIZE is the size of total address space divided by 8 */ +#define KASAN_SHADOW_SIZE ((KASAN_HOST_USER_SPACE_END_ADDR + 1) >> \ + KASAN_SHADOW_SCALE_SHIFT) +#else +#error "KASAN_SHADOW_SIZE is not defined for this sub-architecture" +#endif /* CONFIG_X86_64 */ + +#define KASAN_SHADOW_START (KASAN_SHADOW_OFFSET) +#define KASAN_SHADOW_END (KASAN_SHADOW_START + KASAN_SHADOW_SIZE) + +#ifdef CONFIG_KASAN +void kasan_init(void); +void kasan_map_memory(void *start, unsigned long len); +#else +static inline void kasan_init(void) { } +#endif /* CONFIG_KASAN */ + +#endif /* __ASM_UM_KASAN_H */ diff --git a/arch/um/kernel/dyn.lds.S b/arch/um/kernel/dyn.lds.S index f5001481010c..d91bdb2c3143 100644 --- a/arch/um/kernel/dyn.lds.S +++ b/arch/um/kernel/dyn.lds.S @@ -103,7 +103,10 @@ SECTIONS be empty, which isn't pretty. */ . = ALIGN(32 / 8); .preinit_array : { *(.preinit_array) } - .init_array : { *(.init_array) } + .init_array : { + *(.kasan_init) + *(.init_array) + } .fini_array : { *(.fini_array) } .data : { INIT_TASK_DATA(KERNEL_STACK_SIZE) diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c index 30885d0b94ac..7b0d028aa079 100644 --- a/arch/um/kernel/mem.c +++ b/arch/um/kernel/mem.c @@ -18,6 +18,24 @@ #include <kern_util.h> #include <mem_user.h> #include <os.h> +#include <linux/sched/task.h> + +#ifdef CONFIG_KASAN +void kasan_init(void) +{ + /* + * kasan_map_memory will map all of the required address space and + * the host machine will allocate physical memory as necessary. + */ + kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE); + init_task.kasan_depth = 0; + os_info("KernelAddressSanitizer initialized\n"); +} + +static void (*kasan_init_ptr)(void) +__section(.kasan_init) __used += kasan_init; +#endif /* allocated in paging_init, zeroed in mem_init, and unchanged thereafter */ unsigned long *empty_zero_page = NULL; diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c index 3c1b77474d2d..8530b2e08604 100644 --- a/arch/um/os-Linux/mem.c +++ b/arch/um/os-Linux/mem.c @@ -17,6 +17,28 @@ #include <init.h> #include <os.h> +/* + * kasan_map_memory - maps memory from @start with a size of @len. + * The allocated memory is filled with zeroes upon success. + * @start: the start address of the memory to be mapped + * @len: the length of the memory to be mapped + * + * This function is used to map shadow memory for KASAN in uml + */ +void kasan_map_memory(void *start, size_t len) +{ + if (mmap(start, + len, + PROT_READ|PROT_WRITE, + MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE, + -1, + 0) == MAP_FAILED) { + os_info("Couldn't allocate shadow memory: %s\n.", + strerror(errno)); + exit(1); + } +} + /* Set by make_tempfile() during early boot. */ static char *tempdir = NULL; diff --git a/arch/um/os-Linux/user_syms.c b/arch/um/os-Linux/user_syms.c index 715594fe5719..cb667c9225ab 100644 --- a/arch/um/os-Linux/user_syms.c +++ b/arch/um/os-Linux/user_syms.c @@ -27,10 +27,10 @@ EXPORT_SYMBOL(strstr); #ifndef __x86_64__ extern void *memcpy(void *, const void *, size_t); EXPORT_SYMBOL(memcpy); -#endif - EXPORT_SYMBOL(memmove); EXPORT_SYMBOL(memset); +#endif + EXPORT_SYMBOL(printf); /* Here, instead, I can provide a fake prototype. Yes, someone cares: genksyms. diff --git a/arch/x86/um/Makefile b/arch/x86/um/Makefile index 33c51c064c77..7dbd76c546fe 100644 --- a/arch/x86/um/Makefile +++ b/arch/x86/um/Makefile @@ -26,7 +26,8 @@ else obj-y += syscalls_64.o vdso/ -subarch-y = ../lib/csum-partial_64.o ../lib/memcpy_64.o ../entry/thunk_64.o +subarch-y = ../lib/csum-partial_64.o ../lib/memcpy_64.o ../entry/thunk_64.o \ + ../lib/memmove_64.o ../lib/memset_64.o endif diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile index 0caddd6acb22..450efa0fb694 100644 --- a/arch/x86/um/vdso/Makefile +++ b/arch/x86/um/vdso/Makefile @@ -3,6 +3,9 @@ # Building vDSO images for x86. # +# do not instrument on vdso because KASAN is not compatible with user mode +KASAN_SANITIZE := n + # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in. KCOV_INSTRUMENT := n diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan index 81f5464ea9e1..5b54f3c9a741 100644 --- a/lib/Kconfig.kasan +++ b/lib/Kconfig.kasan @@ -125,7 +125,7 @@ config KASAN_STACK_ENABLE config KASAN_STACK int - default 1 if KASAN_STACK_ENABLE || CC_IS_GCC + default 1 if (KASAN_STACK_ENABLE || CC_IS_GCC) && !UML default 0 config KASAN_S390_4_LEVEL_PAGING -- 2.25.0.265.gbab2e86ba0-goog
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