Messages in this thread Patch in this message | | | Date | Mon, 10 Feb 2020 14:58:06 -0800 | Subject | [RFC PATCH v2] 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 and is based off of "[RFC PATCH] um: implement CONFIG_CONSTRUCTORS for modules" (https://patchwork.ozlabs.org/patch/1234551/) and "[DEMO] um: demonstrate super early constructors" (https://patchwork.ozlabs.org/patch/1234553/) by Johannes.
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 0x100000000000. 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.
Signed-off-by: Patricia Alfonso <trishalfonso@google.com> ---
Changes since v1: - KASAN has been initialized much earlier. - With the help of Johannes's RFC patch to implement constructors in UML and Demo showing how kasan_init could take advantage of these super early constructors, most of the "KASAN_SANITIZE := n" have been removed. - Removed extraneous code - Fixed typos
arch/um/Kconfig | 10 ++++++++++ arch/um/Makefile | 6 ++++++ arch/um/include/asm/dma.h | 1 + arch/um/include/asm/kasan.h | 30 ++++++++++++++++++++++++++++++ arch/um/kernel/Makefile | 22 ++++++++++++++++++++++ arch/um/kernel/mem.c | 19 +++++++++---------- arch/um/os-Linux/mem.c | 19 +++++++++++++++++++ arch/um/os-Linux/user_syms.c | 4 ++-- arch/x86/um/Makefile | 3 ++- arch/x86/um/vdso/Makefile | 3 +++ 10 files changed, 104 insertions(+), 13 deletions(-) create mode 100644 arch/um/include/asm/kasan.h
diff --git a/arch/um/Kconfig b/arch/um/Kconfig index 0917f8443c28..2b76dc273731 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 +201,15 @@ 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 0x100000000000 + help + This is the offset at which the ~2.25TB of shadow memory is + initialized and used by KASAN for memory debugging. The default + is 0x100000000000. + 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/dma.h b/arch/um/include/asm/dma.h index fdc53642c718..8aafd60d62bb 100644 --- a/arch/um/include/asm/dma.h +++ b/arch/um/include/asm/dma.h @@ -5,6 +5,7 @@ #include <asm/io.h> extern unsigned long uml_physmem; +extern unsigned long long physmem_size; #define MAX_DMA_ADDRESS (uml_physmem) diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h new file mode 100644 index 000000000000..ba08061068cf --- /dev/null +++ b/arch/um/include/asm/kasan.h @@ -0,0 +1,30 @@ +/* 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) +#ifdef CONFIG_X86_64 +#define KASAN_SHADOW_SIZE 0x100000000000UL +#else +#error "KASAN_SHADOW_SIZE is not defined for this sub-architecture" +#endif /* CONFIG_X86_64 */ + +// used in kasan_mem_to_shadow to divide by 8 +#define KASAN_SHADOW_SCALE_SHIFT 3 + +#define KASAN_SHADOW_START (KASAN_SHADOW_OFFSET) +#define KASAN_SHADOW_END (KASAN_SHADOW_START + KASAN_SHADOW_SIZE) + +#ifdef CONFIG_KASAN +void kasan_init(void); +#else +static inline void kasan_init(void) { } +#endif /* CONFIG_KASAN */ + +void kasan_map_memory(void *start, unsigned long len); +void kasan_unpoison_shadow(const void *address, size_t size); + +#endif /* __ASM_UM_KASAN_H */ diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile index 5aa882011e04..875e1827588b 100644 --- a/arch/um/kernel/Makefile +++ b/arch/um/kernel/Makefile @@ -8,6 +8,28 @@ # kernel. KCOV_INSTRUMENT := n +# The way UMl deals with the stack causes seemingly false positive KASAN +# reports such as: +# BUG: KASAN: stack-out-of-bounds in show_stack+0x15e/0x1fb +# Read of size 8 at addr 000000006184bbb0 by task swapper/1 +# ================================================================== +# BUG: KASAN: stack-out-of-bounds in dump_trace+0x141/0x1c5 +# Read of size 8 at addr 0000000071057eb8 by task swapper/1 +# ================================================================== +# BUG: KASAN: stack-out-of-bounds in get_wchan+0xd7/0x138 +# Read of size 8 at addr 0000000070e8fc80 by task systemd/1 +# +# With these files removed from instrumentation, those reports are +# eliminated, but KASAN still repeatedly reports a bug on syscall_stub_data: +# ================================================================== +# BUG: KASAN: stack-out-of-bounds in syscall_stub_data+0x299/0x2bf +# Read of size 128 at addr 0000000071457c50 by task swapper/1 + +KASAN_SANITIZE_stacktrace.o := n +KASAN_SANITIZE_sysrq.o := n +KASAN_SANITIZE_process.o := n + + CPPFLAGS_vmlinux.lds := -DSTART=$(LDS_START) \ -DELF_ARCH=$(LDS_ELF_ARCH) \ -DELF_FORMAT=$(LDS_ELF_FORMAT) \ diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c index 32fc941c80f7..7b7b8a0ee724 100644 --- a/arch/um/kernel/mem.c +++ b/arch/um/kernel/mem.c @@ -18,21 +18,20 @@ #include <kern_util.h> #include <mem_user.h> #include <os.h> +#include <linux/sched/task.h> -extern int printf(const char *msg, ...); -static void early_print(void) +#ifdef CONFIG_KASAN +void kasan_init(void) { - printf("I'm super early, before constructors\n"); + kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE); + init_task.kasan_depth = 0; + os_info("KernelAddressSanitizer initialized\n"); } -static void __attribute__((constructor)) constructor_test(void) -{ - printf("yes, you can see it\n"); -} - -static void (*early_print_ptr)(void) +static void (*kasan_init_ptr)(void) __attribute__((section(".kasan_init"), used)) - = early_print; += 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..da7039721d35 100644 --- a/arch/um/os-Linux/mem.c +++ b/arch/um/os-Linux/mem.c @@ -17,6 +17,25 @@ #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", strerror(errno)); +} + /* 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 -- 2.25.0.341.g760bfbb309-goog
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