livepatch: kernel: add support for live patching

This commit introduces code for the live patching core.  It implements
an ftrace-based mechanism and kernel interface for doing live patching
of kernel and kernel module functions.

It represents the greatest common functionality set between kpatch and
kgraft and can accept patches built using either method.

This first version does not implement any consistency mechanism that
ensures that old and new code do not run together.  In practice, ~90% of
CVEs are safe to apply in this way, since they simply add a conditional
check.  However, any function change that can not execute safely with
the old version of the function can _not_ be safely applied in this
version.

[ jkosina@suse.cz: due to the number of contributions that got folded into
  this original patch from Seth Jennings, add SUSE's copyright as well, as
  discussed via e-mail ]

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.cz>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 90 insertions, 0 deletions

diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
new file mode 100644
index 000000000000..ff3c3101d003
--- /dev/null
+++ b/arch/x86/kernel/livepatch.c
@@ -0,0 +1,90 @@
+/*
+ * livepatch.c - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <asm/cacheflush.h>
+#include <asm/page_types.h>
+#include <asm/elf.h>
+#include <asm/livepatch.h>
+
+/**
+ * klp_write_module_reloc() - write a relocation in a module
+ * @mod:	module in which the section to be modified is found
+ * @type:	ELF relocation type (see asm/elf.h)
+ * @loc:	address that the relocation should be written to
+ * @value:	relocation value (sym address + addend)
+ *
+ * This function writes a relocation to the specified location for
+ * a particular module.
+ */
+int klp_write_module_reloc(struct module *mod, unsigned long type,
+			   unsigned long loc, unsigned long value)
+{
+	int ret, numpages, size = 4;
+	bool readonly;
+	unsigned long val;
+	unsigned long core = (unsigned long)mod->module_core;
+	unsigned long core_ro_size = mod->core_ro_size;
+	unsigned long core_size = mod->core_size;
+
+	switch (type) {
+	case R_X86_64_NONE:
+		return 0;
+	case R_X86_64_64:
+		val = value;
+		size = 8;
+		break;
+	case R_X86_64_32:
+		val = (u32)value;
+		break;
+	case R_X86_64_32S:
+		val = (s32)value;
+		break;
+	case R_X86_64_PC32:
+		val = (u32)(value - loc);
+		break;
+	default:
+		/* unsupported relocation type */
+		return -EINVAL;
+	}
+
+	if (loc < core || loc >= core + core_size)
+		/* loc does not point to any symbol inside the module */
+		return -EINVAL;
+
+	if (loc < core + core_ro_size)
+		readonly = true;
+	else
+		readonly = false;
+
+	/* determine if the relocation spans a page boundary */
+	numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
+
+	if (readonly)
+		set_memory_rw(loc & PAGE_MASK, numpages);
+
+	ret = probe_kernel_write((void *)loc, &val, size);
+
+	if (readonly)
+		set_memory_ro(loc & PAGE_MASK, numpages);
+
+	return ret;
+}