Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 asm update from Ingo Molnar:
 "This adds a new SYSRET testcase"

* 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  selftests/x86: Add a selftest for SYSRET to noncanonical addresses

tools/testing/selftests/x86/Makefile

@@ -10,7 +10,7 @@ TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_sysc
 TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault test_syscall_vdso unwind_vdso \
 			test_FCMOV test_FCOMI test_FISTTP \
 			vdso_restorer
-TARGETS_C_64BIT_ONLY := fsgsbase
+TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip
 
 TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
 TARGETS_C_64BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_64BIT_ONLY)

tools/testing/selftests/x86/sysret_rip.c

@@ -0,0 +1,195 @@
+/*
+ * sigreturn.c - tests that x86 avoids Intel SYSRET pitfalls
+ * Copyright (c) 2014-2016 Andrew Lutomirski
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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.
+ */
+
+#define _GNU_SOURCE
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include <sys/signal.h>
+#include <sys/ucontext.h>
+#include <sys/syscall.h>
+#include <err.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <setjmp.h>
+#include <sys/user.h>
+#include <sys/mman.h>
+#include <assert.h>
+
+
+asm (
+	".pushsection \".text\", \"ax\"\n\t"
+	".balign 4096\n\t"
+	"test_page: .globl test_page\n\t"
+	".fill 4094,1,0xcc\n\t"
+	"test_syscall_insn:\n\t"
+	"syscall\n\t"
+	".ifne . - test_page - 4096\n\t"
+	".error \"test page is not one page long\"\n\t"
+	".endif\n\t"
+	".popsection"
+    );
+
+extern const char test_page[];
+static void const *current_test_page_addr = test_page;
+
+static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
+		       int flags)
+{
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_sigaction = handler;
+	sa.sa_flags = SA_SIGINFO | flags;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(sig, &sa, 0))
+		err(1, "sigaction");
+}
+
+static void clearhandler(int sig)
+{
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = SIG_DFL;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(sig, &sa, 0))
+		err(1, "sigaction");
+}
+
+/* State used by our signal handlers. */
+static gregset_t initial_regs;
+
+static volatile unsigned long rip;
+
+static void sigsegv_for_sigreturn_test(int sig, siginfo_t *info, void *ctx_void)
+{
+	ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+	if (rip != ctx->uc_mcontext.gregs[REG_RIP]) {
+		printf("[FAIL]\tRequested RIP=0x%lx but got RIP=0x%lx\n",
+		       rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]);
+		fflush(stdout);
+		_exit(1);
+	}
+
+	memcpy(&ctx->uc_mcontext.gregs, &initial_regs, sizeof(gregset_t));
+
+	printf("[OK]\tGot SIGSEGV at RIP=0x%lx\n", rip);
+}
+
+static void sigusr1(int sig, siginfo_t *info, void *ctx_void)
+{
+	ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+	memcpy(&initial_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
+
+	/* Set IP and CX to match so that SYSRET can happen. */
+	ctx->uc_mcontext.gregs[REG_RIP] = rip;
+	ctx->uc_mcontext.gregs[REG_RCX] = rip;
+
+	/* R11 and EFLAGS should already match. */
+	assert(ctx->uc_mcontext.gregs[REG_EFL] ==
+	       ctx->uc_mcontext.gregs[REG_R11]);
+
+	sethandler(SIGSEGV, sigsegv_for_sigreturn_test, SA_RESETHAND);
+
+	return;
+}
+
+static void test_sigreturn_to(unsigned long ip)
+{
+	rip = ip;
+	printf("[RUN]\tsigreturn to 0x%lx\n", ip);
+	raise(SIGUSR1);
+}
+
+static jmp_buf jmpbuf;
+
+static void sigsegv_for_fallthrough(int sig, siginfo_t *info, void *ctx_void)
+{
+	ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+	if (rip != ctx->uc_mcontext.gregs[REG_RIP]) {
+		printf("[FAIL]\tExpected SIGSEGV at 0x%lx but got RIP=0x%lx\n",
+		       rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]);
+		fflush(stdout);
+		_exit(1);
+	}
+
+	siglongjmp(jmpbuf, 1);
+}
+
+static void test_syscall_fallthrough_to(unsigned long ip)
+{
+	void *new_address = (void *)(ip - 4096);
+	void *ret;
+
+	printf("[RUN]\tTrying a SYSCALL that falls through to 0x%lx\n", ip);
+
+	ret = mremap((void *)current_test_page_addr, 4096, 4096,
+		     MREMAP_MAYMOVE | MREMAP_FIXED, new_address);
+	if (ret == MAP_FAILED) {
+		if (ip <= (1UL << 47) - PAGE_SIZE) {
+			err(1, "mremap to %p", new_address);
+		} else {
+			printf("[OK]\tmremap to %p failed\n", new_address);
+			return;
+		}
+	}
+
+	if (ret != new_address)
+		errx(1, "mremap malfunctioned: asked for %p but got %p\n",
+		     new_address, ret);
+
+	current_test_page_addr = new_address;
+	rip = ip;
+
+	if (sigsetjmp(jmpbuf, 1) == 0) {
+		asm volatile ("call *%[syscall_insn]" :: "a" (SYS_getpid),
+			      [syscall_insn] "rm" (ip - 2));
+		errx(1, "[FAIL]\tSyscall trampoline returned");
+	}
+
+	printf("[OK]\tWe survived\n");
+}
+
+int main()
+{
+	/*
+	 * When the kernel returns from a slow-path syscall, it will
+	 * detect whether SYSRET is appropriate.  If it incorrectly
+	 * thinks that SYSRET is appropriate when RIP is noncanonical,
+	 * it'll crash on Intel CPUs.
+	 */
+	sethandler(SIGUSR1, sigusr1, 0);
+	for (int i = 47; i < 64; i++)
+		test_sigreturn_to(1UL<<i);
+
+	clearhandler(SIGUSR1);
+
+	sethandler(SIGSEGV, sigsegv_for_fallthrough, 0);
+
+	/* One extra test to check that we didn't screw up the mremap logic. */
+	test_syscall_fallthrough_to((1UL << 47) - 2*PAGE_SIZE);
+
+	/* These are the interesting cases. */
+	for (int i = 47; i < 64; i++) {
+		test_syscall_fallthrough_to((1UL<<i) - PAGE_SIZE);
+		test_syscall_fallthrough_to(1UL<<i);
+	}
+
+	return 0;
+}