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![Catalin Marinas](/assets/img/avatar_default.png)
The flush_icache_range() API is meant to be used on kernel addresses only as it may not have the infrastructure (exception entries) to handle user memory faults. The lkdtm execute_user_location() function tests the kernel execution of user space addresses by mmap'ing an anonymous page, copying some code together with cache maintenance and attempting to run it. However, the cache maintenance step may fail because of the incorrect API usage described above. The patch changes lkdtm to use access_process_vm() for copying the code into user space which would take care of the necessary cache maintenance. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> [kees: export access_process_vm() for module use] Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
202 lines
4.6 KiB
C
202 lines
4.6 KiB
C
/*
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* This is for all the tests related to validating kernel memory
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* permissions: non-executable regions, non-writable regions, and
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* even non-readable regions.
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*/
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#include "lkdtm.h"
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/mman.h>
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#include <linux/uaccess.h>
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#include <asm/cacheflush.h>
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/* Whether or not to fill the target memory area with do_nothing(). */
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#define CODE_WRITE true
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#define CODE_AS_IS false
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/* How many bytes to copy to be sure we've copied enough of do_nothing(). */
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#define EXEC_SIZE 64
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/* This is non-const, so it will end up in the .data section. */
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static u8 data_area[EXEC_SIZE];
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/* This is cost, so it will end up in the .rodata section. */
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static const unsigned long rodata = 0xAA55AA55;
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/* This is marked __ro_after_init, so it should ultimately be .rodata. */
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static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
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/*
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* This just returns to the caller. It is designed to be copied into
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* non-executable memory regions.
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*/
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static void do_nothing(void)
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{
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return;
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}
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/* Must immediately follow do_nothing for size calculuations to work out. */
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static void do_overwritten(void)
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{
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pr_info("do_overwritten wasn't overwritten!\n");
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return;
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}
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static noinline void execute_location(void *dst, bool write)
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{
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void (*func)(void) = dst;
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pr_info("attempting ok execution at %p\n", do_nothing);
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do_nothing();
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if (write == CODE_WRITE) {
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memcpy(dst, do_nothing, EXEC_SIZE);
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flush_icache_range((unsigned long)dst,
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(unsigned long)dst + EXEC_SIZE);
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}
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pr_info("attempting bad execution at %p\n", func);
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func();
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}
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static void execute_user_location(void *dst)
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{
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int copied;
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/* Intentionally crossing kernel/user memory boundary. */
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void (*func)(void) = dst;
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pr_info("attempting ok execution at %p\n", do_nothing);
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do_nothing();
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copied = access_process_vm(current, (unsigned long)dst, do_nothing,
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EXEC_SIZE, FOLL_WRITE);
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if (copied < EXEC_SIZE)
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return;
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pr_info("attempting bad execution at %p\n", func);
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func();
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}
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void lkdtm_WRITE_RO(void)
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{
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/* Explicitly cast away "const" for the test. */
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unsigned long *ptr = (unsigned long *)&rodata;
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pr_info("attempting bad rodata write at %p\n", ptr);
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*ptr ^= 0xabcd1234;
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}
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void lkdtm_WRITE_RO_AFTER_INIT(void)
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{
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unsigned long *ptr = &ro_after_init;
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/*
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* Verify we were written to during init. Since an Oops
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* is considered a "success", a failure is to just skip the
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* real test.
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*/
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if ((*ptr & 0xAA) != 0xAA) {
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pr_info("%p was NOT written during init!?\n", ptr);
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return;
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}
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pr_info("attempting bad ro_after_init write at %p\n", ptr);
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*ptr ^= 0xabcd1234;
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}
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void lkdtm_WRITE_KERN(void)
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{
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size_t size;
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unsigned char *ptr;
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size = (unsigned long)do_overwritten - (unsigned long)do_nothing;
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ptr = (unsigned char *)do_overwritten;
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pr_info("attempting bad %zu byte write at %p\n", size, ptr);
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memcpy(ptr, (unsigned char *)do_nothing, size);
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flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size));
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do_overwritten();
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}
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void lkdtm_EXEC_DATA(void)
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{
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execute_location(data_area, CODE_WRITE);
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}
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void lkdtm_EXEC_STACK(void)
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{
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u8 stack_area[EXEC_SIZE];
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execute_location(stack_area, CODE_WRITE);
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}
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void lkdtm_EXEC_KMALLOC(void)
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{
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u32 *kmalloc_area = kmalloc(EXEC_SIZE, GFP_KERNEL);
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execute_location(kmalloc_area, CODE_WRITE);
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kfree(kmalloc_area);
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}
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void lkdtm_EXEC_VMALLOC(void)
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{
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u32 *vmalloc_area = vmalloc(EXEC_SIZE);
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execute_location(vmalloc_area, CODE_WRITE);
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vfree(vmalloc_area);
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}
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void lkdtm_EXEC_RODATA(void)
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{
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execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
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}
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void lkdtm_EXEC_USERSPACE(void)
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{
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unsigned long user_addr;
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user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_ANONYMOUS | MAP_PRIVATE, 0);
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if (user_addr >= TASK_SIZE) {
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pr_warn("Failed to allocate user memory\n");
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return;
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}
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execute_user_location((void *)user_addr);
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vm_munmap(user_addr, PAGE_SIZE);
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}
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void lkdtm_ACCESS_USERSPACE(void)
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{
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unsigned long user_addr, tmp = 0;
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unsigned long *ptr;
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user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_ANONYMOUS | MAP_PRIVATE, 0);
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if (user_addr >= TASK_SIZE) {
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pr_warn("Failed to allocate user memory\n");
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return;
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}
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if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) {
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pr_warn("copy_to_user failed\n");
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vm_munmap(user_addr, PAGE_SIZE);
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return;
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}
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ptr = (unsigned long *)user_addr;
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pr_info("attempting bad read at %p\n", ptr);
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tmp = *ptr;
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tmp += 0xc0dec0de;
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pr_info("attempting bad write at %p\n", ptr);
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*ptr = tmp;
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vm_munmap(user_addr, PAGE_SIZE);
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}
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void __init lkdtm_perms_init(void)
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{
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/* Make sure we can write to __ro_after_init values during __init */
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ro_after_init |= 0xAA;
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}
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