[PATCH 05/10] lkdtm: disable set_fs-based tests for !CONFIG_SET_FS

Christoph Hellwig
2020-08-27T15:09:29Z

Once we can't manipulate the address limit, we also can't test what
happens when the manipulation is abused.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
drivers/misc/lkdtm/bugs.c | 4 ++++
drivers/misc/lkdtm/usercopy.c | 4 ++++
2 files changed, 8 insertions(+)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 4dfbfd51bdf774..0d5b93694a0183 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -315,11 +315,15 @@ void lkdtm_CORRUPT_LIST_DEL(void)
/* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */
void lkdtm_CORRUPT_USER_DS(void)
{
+#ifdef CONFIG_SET_FS
pr_info("setting bad task size limit\n");
set_fs(KERNEL_DS);

/* Make sure we do not keep running with a KERNEL_DS! */
force_sig(SIGKILL);
+#else
+ pr_err("XFAIL: this requires set_fs()\n");
+#endif
}

/* Test that VMAP_STACK is actually allocating with a leading guard page */
diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index b833367a45d053..04d10063835241 100644
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -327,6 +327,7 @@ void lkdtm_USERCOPY_KERNEL(void)

void lkdtm_USERCOPY_KERNEL_DS(void)
{
+#ifdef CONFIG_SET_FS
char __user *user_ptr =
(char __user *)(0xFUL << (sizeof(unsigned long) * 8 - 4));
mm_segment_t old_fs = get_fs();
@@ -338,6 +339,9 @@ void lkdtm_USERCOPY_KERNEL_DS(void)
if (copy_to_user(user_ptr, buf, sizeof(buf)) == 0)
pr_err("copy_to_user() to noncanonical address succeeded!?\n");
set_fs(old_fs);
+#else
+ pr_err("XFAIL: this requires set_fs()\n");
+#endif
}

void __init lkdtm_usercopy_init(void)
--
2.28.0