linux-kernel - [PATCH 05/10] lkdtm: disable set_fs-based tests for !CONFIG_SET

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Message-Id: <20200827150030.282762-6-hch@lst.de>
Date:   Thu, 27 Aug 2020 17:00:25 +0200
From:   Christoph Hellwig <hch@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>, x86@...nel.org
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 05/10] lkdtm: disable set_fs-based tests for !CONFIG_SET_FS

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@....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