Messages in this thread Patch in this message | | | Subject | Re: [PATCH] UML: add support for KASAN under x86_64 | From | Johannes Berg <> | Date | Wed, 11 Mar 2020 12:18:53 +0100 |
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On Wed, 2020-03-11 at 11:32 +0100, Johannes Berg wrote: > > I do see issues with modules though, e.g. > https://p.sipsolutions.net/1a2df5f65d885937.txt > > where we seem to get some real confusion when lockdep is storing the > stack trace?? > > And https://p.sipsolutions.net/9a97e8f68d8d24b7.txt, where something > convinces ASAN that an address is a user address (it might even be > right?) and it disallows kernel access to it?
I can work around both of these by not freeing the original module copy in kernel/module.c:
/* Get rid of temporary copy. */ // free_copy(info);
but I really have no idea why we get this in the first place?
Another interesting data point is that it never happens on the first module.
Also, I've managed to get a report like this:
Memory state around the buggy address: 000000007106cf00: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 000000007106cf80: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >000000007106d000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b ^ 000000007106d080: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 000000007106d100: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
which indicates that something's _really_ off with the KASAN shadow?
Ohhh ...
$ gdb -p ... (gdb) p/x task_size $1 = 0x7fc0000000 (gdb) p/x __end_of_fixed_addresses $2 = 0x0 (gdb) p/x end_iomem $3 = 0x70000000 (gdb) p/x __va_space
#define TASK_SIZE (task_size) #define FIXADDR_TOP (TASK_SIZE - 2 * PAGE_SIZE)
#define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE) #define FIXADDR_SIZE (__end_of_fixed_addresses << PAGE_SHIFT)
#define VMALLOC_END (FIXADDR_START-2*PAGE_SIZE)
#define MODULES_VADDR VMALLOC_START #define MODULES_END VMALLOC_END #define VMALLOC_START ((end_iomem + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1)) #define VMALLOC_OFFSET (__va_space) #define __va_space (8*1024*1024)
So from that, it would look like the UML vmalloc area is from 0x 70800000 all the way to 0x7fbfffc000, which obviously clashes with the KASAN_SHADOW_OFFSET being just 0x7fff8000.
I'm guessing that basically the module loading overwrote the kasan shadow then?
I tried changing it
config KASAN_SHADOW_OFFSET hex depends on KASAN - default 0x7fff8000 + default 0x8000000000
and also put a check in like this:
+++ b/arch/um/kernel/um_arch.c @@ -13,6 +13,7 @@ #include <linux/sched.h> #include <linux/sched/task.h> #include <linux/kmsg_dump.h> +#include <linux/kasan.h> #include <asm/pgtable.h> #include <asm/processor.h> @@ -267,9 +268,11 @@ int __init linux_main(int argc, char **argv) /* * TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps * out */ task_size = host_task_size & PGDIR_MASK; + if (task_size > KASAN_SHADOW_OFFSET) + panic("KASAN shadow offset must be bigger than task size");
but now I just crash accessing the shadow even though it was mapped fine?
Pid: 504, comm: modprobe Tainted: G O 5.5.0-rc6-00009-g09462ab4014b-dirty RIP: RSP: 000000006d68fa90 EFLAGS: 00010202 RAX: 000000800e0210cd RBX: 000000007010866f RCX: 00000000601a9777 RDX: 000000800e0210ce RSI: 0000000000000004 RDI: 000000007010866c RBP: 000000006d68faa0 R08: 000000800e0210cd R09: 0000000060041432 R10: 000000800e0210ce R11: 0000000000000001 R12: 000000800e0210cd R13: 0000000000000000 R14: 0000000000000001 R15: 00000000601c2e82 Kernel panic - not syncing: Kernel mode fault at addr 0x800e0210cd, ip 0x601c332b CPU: 0 PID: 504 Comm: modprobe Tainted: G O 5.5.0-rc6-00009-g09462ab4014b-dirty #24 Stack: 601c2f89 70108638 6d68fab0 601c1209 6d68fad0 601a9777 6cf2b240 7317f000 6d68fb40 601a2ae9 6f15b118 00000001 Call Trace: ? __asan_load8 (/home/tester/vlab/linux/mm/kasan/generic.c:252) __kasan_check_write (/home/tester/vlab/linux/mm/kasan/common.c:102) __free_pages (/home/tester/vlab/linux/./arch/x86/include/asm/atomic.h:125 /home/tester/vlab/linux/./include/asm-generic/atomic-instrumented.h:748 /home/tester/vlab/linux/./include/linux/page_ref.h:139 /home/tester/vlab/linux/./include/linux/mm.h:593 /home/tester/vlab/linux/mm/page_alloc.c:4823) __vunmap (/home/tester/vlab/linux/mm/vmalloc.c:2303 (discriminator 2)) ? __asan_load4 (/home/tester/vlab/linux/mm/kasan/generic.c:251) ? sysfs_create_bin_file (/home/tester/vlab/linux/fs/sysfs/file.c:537) __vfree (/home/tester/vlab/linux/mm/vmalloc.c:2356) ? delete_object_full (/home/tester/vlab/linux/mm/kmemleak.c:693) vfree (/home/tester/vlab/linux/mm/vmalloc.c:2386) ? sysfs_create_bin_file (/home/tester/vlab/linux/fs/sysfs/file.c:537) ? __asan_load8 (/home/tester/vlab/linux/mm/kasan/generic.c:252) load_module (/home/tester/vlab/linux/./include/linux/jump_label.h:254 /home/tester/vlab/linux/./include/linux/jump_label.h:264 /home/tester/vlab/linux/./include/trace/events/module.h:31 /home/tester/vlab/linux/kernel/module.c:3927) ? kernel_read_file_from_fd (/home/tester/vlab/linux/fs/exec.c:993) ? __asan_load8 (/home/tester/vlab/linux/mm/kasan/generic.c:252) __do_sys_finit_module (/home/tester/vlab/linux/kernel/module.c:4019) ? sys_finit_module (/home/tester/vlab/linux/kernel/module.c:3995) ? __asan_store8 (/home/tester/vlab/linux/mm/kasan/generic.c:252) sys_finit_module (/home/tester/vlab/linux/kernel/module.c:3995) handle_syscall (/home/tester/vlab/linux/arch/um/kernel/skas/syscall.c:44) userspace (/home/tester/vlab/linux/arch/um/os-Linux/skas/process.c:173 /home/tester/vlab/linux/arch/um/os-Linux/skas/process.c:416) ? save_registers (/home/tester/vlab/linux/arch/um/os-Linux/registers.c:18) ? arch_prctl (/home/tester/vlab/linux/arch/x86/um/syscalls_64.c:65) ? calculate_sigpending (/home/tester/vlab/linux/kernel/signal.c:200) ? __asan_load8 (/home/tester/vlab/linux/mm/kasan/generic.c:252) ? __asan_load8 (/home/tester/vlab/linux/mm/kasan/generic.c:252) ? __asan_load8 (/home/tester/vlab/linux/mm/kasan/generic.c:252) fork_handler (/home/tester/vlab/linux/arch/um/kernel/process.c:154) johannes
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