openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 202 insertions, 0 deletions

diff --git a/drivers/misc/lkdtm/cfi.c b/drivers/misc/lkdtm/cfi.c
new file mode 100644
index 000000000..c3971f7ca
--- /dev/null
+++ b/drivers/misc/lkdtm/cfi.c
@@ -0,0 +1,202 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This is for all the tests relating directly to Control Flow Integrity.
+ */
+#include "lkdtm.h"
+#include <asm/page.h>
+
+static int called_count;
+
+/* Function taking one argument, without a return value. */
+static noinline void lkdtm_increment_void(int *counter)
+{
+	(*counter)++;
+}
+
+/* Function taking one argument, returning int. */
+static noinline int lkdtm_increment_int(int *counter)
+{
+	(*counter)++;
+
+	return *counter;
+}
+
+/* Don't allow the compiler to inline the calls. */
+static noinline void lkdtm_indirect_call(void (*func)(int *))
+{
+	func(&called_count);
+}
+
+/*
+ * This tries to call an indirect function with a mismatched prototype.
+ */
+static void lkdtm_CFI_FORWARD_PROTO(void)
+{
+	/*
+	 * Matches lkdtm_increment_void()'s prototype, but not
+	 * lkdtm_increment_int()'s prototype.
+	 */
+	pr_info("Calling matched prototype ...\n");
+	lkdtm_indirect_call(lkdtm_increment_void);
+
+	pr_info("Calling mismatched prototype ...\n");
+	lkdtm_indirect_call((void *)lkdtm_increment_int);
+
+	pr_err("FAIL: survived mismatched prototype function call!\n");
+	pr_expected_config(CONFIG_CFI);
+}
+
+/*
+ * This can stay local to LKDTM, as there should not be a production reason
+ * to disable PAC && SCS.
+ */
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
+# ifdef CONFIG_ARM64_BTI_KERNEL
+#  define __no_pac             "branch-protection=bti"
+# else
+#  ifdef CONFIG_CC_HAS_BRANCH_PROT_PAC_RET
+#   define __no_pac            "branch-protection=none"
+#  else
+#   define __no_pac            "sign-return-address=none"
+#  endif
+# endif
+# define __no_ret_protection   __noscs __attribute__((__target__(__no_pac)))
+#else
+# define __no_ret_protection   __noscs
+#endif
+
+#define no_pac_addr(addr)      \
+	((__force __typeof__(addr))((uintptr_t)(addr) | PAGE_OFFSET))
+
+#ifdef CONFIG_RISCV
+/* https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc#frame-pointer-convention */
+#define FRAME_RA_OFFSET		(-1)
+#else
+#define FRAME_RA_OFFSET		1
+#endif
+
+/* The ultimate ROP gadget. */
+static noinline __no_ret_protection
+void set_return_addr_unchecked(unsigned long *expected, unsigned long *addr)
+{
+	/* Use of volatile is to make sure final write isn't seen as a dead store. */
+	unsigned long * volatile *ret_addr =
+		(unsigned long **)__builtin_frame_address(0) + FRAME_RA_OFFSET;
+
+	/* Make sure we've found the right place on the stack before writing it. */
+	if (no_pac_addr(*ret_addr) == expected)
+		*ret_addr = (addr);
+	else
+		/* Check architecture, stack layout, or compiler behavior... */
+		pr_warn("Eek: return address mismatch! %px != %px\n",
+			*ret_addr, addr);
+}
+
+static noinline
+void set_return_addr(unsigned long *expected, unsigned long *addr)
+{
+	/* Use of volatile is to make sure final write isn't seen as a dead store. */
+	unsigned long * volatile *ret_addr =
+		(unsigned long **)__builtin_frame_address(0) + FRAME_RA_OFFSET;
+
+	/* Make sure we've found the right place on the stack before writing it. */
+	if (no_pac_addr(*ret_addr) == expected)
+		*ret_addr = (addr);
+	else
+		/* Check architecture, stack layout, or compiler behavior... */
+		pr_warn("Eek: return address mismatch! %px != %px\n",
+			*ret_addr, addr);
+}
+
+static volatile int force_check;
+
+static void lkdtm_CFI_BACKWARD(void)
+{
+	/* Use calculated gotos to keep labels addressable. */
+	void *labels[] = { NULL, &&normal, &&redirected, &&check_normal, &&check_redirected };
+
+	pr_info("Attempting unchecked stack return address redirection ...\n");
+
+	/* Always false */
+	if (force_check) {
+		/*
+		 * Prepare to call with NULLs to avoid parameters being treated as
+		 * constants in -02.
+		 */
+		set_return_addr_unchecked(NULL, NULL);
+		set_return_addr(NULL, NULL);
+		if (force_check)
+			goto *labels[1];
+		if (force_check)
+			goto *labels[2];
+		if (force_check)
+			goto *labels[3];
+		if (force_check)
+			goto *labels[4];
+		return;
+	}
+
+	/*
+	 * Use fallthrough switch case to keep basic block ordering between
+	 * set_return_addr*() and the label after it.
+	 */
+	switch (force_check) {
+	case 0:
+		set_return_addr_unchecked(&&normal, &&redirected);
+		fallthrough;
+	case 1:
+normal:
+		/* Always true */
+		if (!force_check) {
+			pr_err("FAIL: stack return address manipulation failed!\n");
+			/* If we can't redirect "normally", we can't test mitigations. */
+			return;
+		}
+		break;
+	default:
+redirected:
+		pr_info("ok: redirected stack return address.\n");
+		break;
+	}
+
+	pr_info("Attempting checked stack return address redirection ...\n");
+
+	switch (force_check) {
+	case 0:
+		set_return_addr(&&check_normal, &&check_redirected);
+		fallthrough;
+	case 1:
+check_normal:
+		/* Always true */
+		if (!force_check) {
+			pr_info("ok: control flow unchanged.\n");
+			return;
+		}
+
+check_redirected:
+		pr_err("FAIL: stack return address was redirected!\n");
+		break;
+	}
+
+	if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) {
+		pr_expected_config(CONFIG_ARM64_PTR_AUTH_KERNEL);
+		return;
+	}
+	if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) {
+		pr_expected_config(CONFIG_SHADOW_CALL_STACK);
+		return;
+	}
+	pr_warn("This is probably expected, since this %s was built *without* %s=y nor %s=y\n",
+		lkdtm_kernel_info,
+		"CONFIG_ARM64_PTR_AUTH_KERNEL", "CONFIG_SHADOW_CALL_STACK");
+}
+
+static struct crashtype crashtypes[] = {
+	CRASHTYPE(CFI_FORWARD_PROTO),
+	CRASHTYPE(CFI_BACKWARD),
+};
+
+struct crashtype_category cfi_crashtypes = {
+	.crashtypes = crashtypes,
+	.len	    = ARRAY_SIZE(crashtypes),
+};