linux-hardening - [PATCH] lkdtm/usercopy: Check vmalloc and >0-order folios

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Message-Id: <20220517214914.878350-1-keescook@chromium.org>
Date:   Tue, 17 May 2022 14:49:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] lkdtm/usercopy: Check vmalloc and >0-order folios

Add coverage for the recently added usercopy checks for vmalloc and
folios, via USERCOPY_VMALLOC and USERCOPY_FOLIO respectively.

Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
Cc: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/misc/lkdtm/usercopy.c | 83 +++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index 945806db2a13..6215ec995cd3 100644
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -5,6 +5,7 @@
  */
 #include "lkdtm.h"
 #include <linux/slab.h>
+#include <linux/highmem.h>
 #include <linux/vmalloc.h>
 #include <linux/sched/task_stack.h>
 #include <linux/mman.h>
@@ -341,6 +342,86 @@ static void lkdtm_USERCOPY_KERNEL(void)
 	vm_munmap(user_addr, PAGE_SIZE);
 }
 
+/*
+ * This expects "kaddr" to point to a PAGE_SIZE allocation, which means
+ * a more complete test that would include copy_from_user() would risk
+ * memory corruption. Just test copy_to_user() here, as that exercises
+ * almost exactly the same code paths.
+ */
+static void do_usercopy_page_span(const char *name, void *kaddr)
+{
+	unsigned long uaddr;
+
+	uaddr = vm_mmap(NULL, 0, PAGE_SIZE, PROT_READ | PROT_WRITE,
+			MAP_ANONYMOUS | MAP_PRIVATE, 0);
+	if (uaddr >= TASK_SIZE) {
+		pr_warn("Failed to allocate user memory\n");
+		return;
+	}
+
+	/* Initialize contents. */
+	memset(kaddr, 0xAA, PAGE_SIZE);
+
+	/* Bump the kaddr forward to detect a page-spanning overflow. */
+	kaddr += PAGE_SIZE / 2;
+
+	pr_info("attempting good copy_to_user() from kernel %s: %px\n",
+		name, kaddr);
+	if (copy_to_user((void __user *)uaddr, kaddr,
+			 unconst + (PAGE_SIZE / 2))) {
+		pr_err("copy_to_user() failed unexpectedly?!\n");
+		goto free_user;
+	}
+
+	pr_info("attempting bad copy_to_user() from kernel %s: %px\n",
+		name, kaddr);
+	if (copy_to_user((void __user *)uaddr, kaddr, unconst + PAGE_SIZE)) {
+		pr_warn("Good, copy_to_user() failed, but lacked Oops(?!)\n");
+		goto free_user;
+	}
+
+	pr_err("FAIL: bad copy_to_user() not detected!\n");
+	pr_expected_config_param(CONFIG_HARDENED_USERCOPY, "hardened_usercopy");
+
+free_user:
+	vm_munmap(uaddr, PAGE_SIZE);
+}
+
+static void lkdtm_USERCOPY_VMALLOC(void)
+{
+	void *addr;
+
+	addr = vmalloc(PAGE_SIZE);
+	if (!addr) {
+		pr_err("vmalloc() failed!?\n");
+		return;
+	}
+	do_usercopy_page_span("vmalloc", addr);
+	vfree(addr);
+}
+
+static void lkdtm_USERCOPY_FOLIO(void)
+{
+	struct folio *folio;
+	void *addr;
+
+	/*
+	 * FIXME: Folio checking currently misses 0-order allocations, so
+	 * allocate and bump forward to the last page.
+	 */
+	folio = folio_alloc(GFP_KERNEL | __GFP_ZERO, 1);
+	if (!folio) {
+		pr_err("folio_alloc() failed!?\n");
+		return;
+	}
+	addr = folio_address(folio);
+	if (addr)
+		do_usercopy_page_span("folio", addr + PAGE_SIZE);
+	else
+		pr_err("folio_address() failed?!\n");
+	folio_put(folio);
+}
+
 void __init lkdtm_usercopy_init(void)
 {
 	/* Prepare cache that lacks SLAB_USERCOPY flag. */
@@ -365,6 +446,8 @@ static struct crashtype crashtypes[] = {
 	CRASHTYPE(USERCOPY_STACK_FRAME_TO),
 	CRASHTYPE(USERCOPY_STACK_FRAME_FROM),
 	CRASHTYPE(USERCOPY_STACK_BEYOND),
+	CRASHTYPE(USERCOPY_VMALLOC),
+	CRASHTYPE(USERCOPY_FOLIO),
 	CRASHTYPE(USERCOPY_KERNEL),
 };
 
-- 
2.32.0