1 files changed, 251 insertions, 0 deletions
diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
new file mode 100644
index 000000000000..e5275d6e674d
--- /dev/null
+++ b/arch/x86/kernel/callthunks.c
@@ -0,0 +1,251 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#define pr_fmt(fmt) "callthunks: " fmt
+
+#include <linux/kallsyms.h>
+#include <linux/memory.h>
+#include <linux/moduleloader.h>
+
+#include <asm/alternative.h>
+#include <asm/cpu.h>
+#include <asm/ftrace.h>
+#include <asm/insn.h>
+#include <asm/kexec.h>
+#include <asm/nospec-branch.h>
+#include <asm/paravirt.h>
+#include <asm/sections.h>
+#include <asm/switch_to.h>
+#include <asm/sync_core.h>
+#include <asm/text-patching.h>
+#include <asm/xen/hypercall.h>
+
+static int __initdata_or_module debug_callthunks;
+
+#define prdbg(fmt, args...)					\
+do {								\
+	if (debug_callthunks)					\
+		printk(KERN_DEBUG pr_fmt(fmt), ##args);		\
+} while(0)
+
+static int __init debug_thunks(char *str)
+{
+	debug_callthunks = 1;
+	return 1;
+}
+__setup("debug-callthunks", debug_thunks);
+
+extern s32 __call_sites[], __call_sites_end[];
+
+struct thunk_desc {
+	void		*template;
+	unsigned int	template_size;
+};
+
+struct core_text {
+	unsigned long	base;
+	unsigned long	end;
+	const char	*name;
+};
+
+static bool thunks_initialized __ro_after_init;
+
+static const struct core_text builtin_coretext = {
+	.base = (unsigned long)_text,
+	.end  = (unsigned long)_etext,
+	.name = "builtin",
+};
+
+static struct thunk_desc callthunk_desc __ro_after_init;
+
+extern void error_entry(void);
+extern void xen_error_entry(void);
+extern void paranoid_entry(void);
+
+static inline bool within_coretext(const struct core_text *ct, void *addr)
+{
+	unsigned long p = (unsigned long)addr;
+
+	return ct->base <= p && p < ct->end;
+}
+
+static inline bool within_module_coretext(void *addr)
+{
+	bool ret = false;
+
+#ifdef CONFIG_MODULES
+	struct module *mod;
+
+	preempt_disable();
+	mod = __module_address((unsigned long)addr);
+	if (mod && within_module_core((unsigned long)addr, mod))
+		ret = true;
+	preempt_enable();
+#endif
+	return ret;
+}
+
+static bool is_coretext(const struct core_text *ct, void *addr)
+{
+	if (ct && within_coretext(ct, addr))
+		return true;
+	if (within_coretext(&builtin_coretext, addr))
+		return true;
+	return within_module_coretext(addr);
+}
+
+static __init_or_module bool skip_addr(void *dest)
+{
+	if (dest == error_entry)
+		return true;
+	if (dest == paranoid_entry)
+		return true;
+	if (dest == xen_error_entry)
+		return true;
+	/* Does FILL_RSB... */
+	if (dest == __switch_to_asm)
+		return true;
+	/* Accounts directly */
+	if (dest == ret_from_fork)
+		return true;
+#ifdef CONFIG_HOTPLUG_CPU
+	if (dest == start_cpu0)
+		return true;
+#endif
+#ifdef CONFIG_FUNCTION_TRACER
+	if (dest == __fentry__)
+		return true;
+#endif
+#ifdef CONFIG_KEXEC_CORE
+	if (dest >= (void *)relocate_kernel &&
+	    dest < (void*)relocate_kernel + KEXEC_CONTROL_CODE_MAX_SIZE)
+		return true;
+#endif
+#ifdef CONFIG_XEN
+	if (dest >= (void *)hypercall_page &&
+	    dest < (void*)hypercall_page + PAGE_SIZE)
+		return true;
+#endif
+	return false;
+}
+
+static __init_or_module void *call_get_dest(void *addr)
+{
+	struct insn insn;
+	void *dest;
+	int ret;
+
+	ret = insn_decode_kernel(&insn, addr);
+	if (ret)
+		return ERR_PTR(ret);
+
+	/* Patched out call? */
+	if (insn.opcode.bytes[0] != CALL_INSN_OPCODE)
+		return NULL;
+
+	dest = addr + insn.length + insn.immediate.value;
+	if (skip_addr(dest))
+		return NULL;
+	return dest;
+}
+
+static const u8 nops[] = {
+	0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90,
+	0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90,
+	0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90,
+	0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90,
+};
+
+static __init_or_module void *patch_dest(void *dest, bool direct)
+{
+	unsigned int tsize = callthunk_desc.template_size;
+	u8 *pad = dest - tsize;
+
+	/* Already patched? */
+	if (!bcmp(pad, callthunk_desc.template, tsize))
+		return pad;
+
+	/* Ensure there are nops */
+	if (bcmp(pad, nops, tsize)) {
+		pr_warn_once("Invalid padding area for %pS\n", dest);
+		return NULL;
+	}
+
+	if (direct)
+		memcpy(pad, callthunk_desc.template, tsize);
+	else
+		text_poke_copy_locked(pad, callthunk_desc.template, tsize, true);
+	return pad;
+}
+
+static __init_or_module void patch_call(void *addr, const struct core_text *ct)
+{
+	void *pad, *dest;
+	u8 bytes[8];
+
+	if (!within_coretext(ct, addr))
+		return;
+
+	dest = call_get_dest(addr);
+	if (!dest || WARN_ON_ONCE(IS_ERR(dest)))
+		return;
+
+	if (!is_coretext(ct, dest))
+		return;
+
+	pad = patch_dest(dest, within_coretext(ct, dest));
+	if (!pad)
+		return;
+
+	prdbg("Patch call at: %pS %px to %pS %px -> %px \n", addr, addr,
+		dest, dest, pad);
+	__text_gen_insn(bytes, CALL_INSN_OPCODE, addr, pad, CALL_INSN_SIZE);
+	text_poke_early(addr, bytes, CALL_INSN_SIZE);
+}
+
+static __init_or_module void
+patch_call_sites(s32 *start, s32 *end, const struct core_text *ct)
+{
+	s32 *s;
+
+	for (s = start; s < end; s++)
+		patch_call((void *)s + *s, ct);
+}
+
+static __init_or_module void
+patch_paravirt_call_sites(struct paravirt_patch_site *start,
+			  struct paravirt_patch_site *end,
+			  const struct core_text *ct)
+{
+	struct paravirt_patch_site *p;
+
+	for (p = start; p < end; p++)
+		patch_call(p->instr, ct);
+}
+
+static __init_or_module void
+callthunks_setup(struct callthunk_sites *cs, const struct core_text *ct)
+{
+	prdbg("Patching call sites %s\n", ct->name);
+	patch_call_sites(cs->call_start, cs->call_end, ct);
+	patch_paravirt_call_sites(cs->pv_start, cs->pv_end, ct);
+	prdbg("Patching call sites done%s\n", ct->name);
+}
+
+void __init callthunks_patch_builtin_calls(void)
+{
+	struct callthunk_sites cs = {
+		.call_start	= __call_sites,
+		.call_end	= __call_sites_end,
+		.pv_start	= __parainstructions,
+		.pv_end		= __parainstructions_end
+	};
+
+	if (!cpu_feature_enabled(X86_FEATURE_CALL_DEPTH))
+		return;
+
+	pr_info("Setting up call depth tracking\n");
+	mutex_lock(&text_mutex);
+	callthunks_setup(&cs, &builtin_coretext);
+	thunks_initialized = true;
+	mutex_unlock(&text_mutex);
+}