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Subject[PATCH] lkdtm: fix ACCESS_USERSPACE test
Date
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>
---
drivers/misc/lkdtm.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
index b5abe34..11fdadc 100644
--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -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);
--
2.4.3


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