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lkdtm: fix ACCESS_USERSPACE test

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Add a copy_to_user() call to the ACCESS_USERSPACE test
prior to attempting direct dereferencing of the user
address to ensure the page is present.  Otherwise,
a fault occurs on arm kernels even prior to the introduction
of CONFIG_CPU_SW_DOMAIN_PAN, and there is no difference in
behavior for CONFIG_CPU_SW_DOMAIN_PAN=n vs CONFIG_CPU_SW_DOMAIN_PAN=y.

Before this change, for any value of CONFIG_CPU_SW_DOMAIN_PAN:
lkdtm: Performing direct entry ACCESS_USERSPACE
lkdtm: attempting bad read at b6fe8000
Unable to handle kernel paging request at virtual address b6fe8000

After this change, for CONFIG_CPU_SW_DOMAIN_PAN=n:
lkdtm: Performing direct entry ACCESS_USERSPACE
lkdtm: attempting bad read at b6efc000
lkdtm: attempting bad write at b6efc000

After this change, for CONFIG_CPU_SW_DOMAIN_PAN=y:
lkdtm: Performing direct entry ACCESS_USERSPACE
lkdtm: attempting bad read at b6f7d000
Unhandled fault: page domain fault (0x01b) at 0xb6f7d000
...

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Stephen Smalley 2015-10-27 16:47:53 -04:00 committed by Greg Kroah-Hartman
parent 169883a63e
commit 2cb202c188
1 changed files with 7 additions and 1 deletions
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8
drivers/misc/lkdtm.c
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@ -472,7 +472,7 @@ static void lkdtm_do_action(enum ctype which)
break;
}
case CT_ACCESS_USERSPACE: {
unsigned long user_addr, tmp;
unsigned long user_addr, tmp = 0;
unsigned long *ptr;
user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
@ -483,6 +483,12 @@ static void lkdtm_do_action(enum ctype which)
return;
}
if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) {
pr_warn("copy_to_user failed\n");
vm_munmap(user_addr, PAGE_SIZE);
return;
}
ptr = (unsigned long *)user_addr;
pr_info("attempting bad read at %p\n", ptr);