6c84bdde8311f7b69f4db7f89c9a4ea6e228be61443c11e67928ea68.patch

From a5652bff891e2feb6f84baca3723b168a37d65b1 Mon Sep 17 00:00:00 2001
From: Guenter Roeck <groeck@chromium.org>
Date: Fri, 21 Sep 2018 12:42:54 -0700
Subject: [PATCH] CHROMIUM: x86: Add alt-syscall support

BUG=chromium:885330
TEST=Boot with alt-syscall enabled

Change-Id: I4a6fd929d46f0cd1ae2aca748e8befb87affabac
Signed-off-by: Guenter Roeck <groeck@chromium.org>

Conflicts (x86 32-bit API changes):
	arch/x86/Kconfig
	arch/x86/entry/common.c

[rebase54(groeck): Address conflicts; squashed:
	CHROMIUM: Restrict ALT_SYSCALL code to 64 bit builds
	CHROMIUM: alt-syscall: Remove entries for x86_32
]
Signed-off-by: Guenter Roeck <groeck@chromium.org>
[rebase510(groeck): Major conflicts; took patch from continuous rebase]
Signed-off-by: Guenter Roeck <groeck@chromium.org>
Change-Id: Ic8548898ae64d8bda70712be3668a2873e59f8e1
---
 arch/x86/Kconfig                   |  1 +
 arch/x86/entry/common.c            | 22 +++++++++-
 arch/x86/include/asm/syscall.h     |  1 +
 arch/x86/include/asm/thread_info.h | 35 +++++++++++++++
 arch/x86/kernel/Makefile           |  3 ++
 arch/x86/kernel/alt-syscall.c      | 70 ++++++++++++++++++++++++++++++
 security/chromiumos/Kconfig        |  1 -
 7 files changed, 131 insertions(+), 2 deletions(-)
 create mode 100644 arch/x86/kernel/alt-syscall.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 49270655e827..4d9fd6c0b39d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -267,6 +267,7 @@ config X86
 	select X86_FEATURE_NAMES		if PROC_FS
 	select PROC_PID_ARCH_STATUS		if PROC_FS
 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT    if EFI
+	select ARCH_HAS_ALT_SYSCALL		if X86_64
 
 config INSTRUCTION_DECODER
 	def_bool y
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 6c2826417b33..fd60091303ac 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -44,13 +44,26 @@ static __always_inline bool do_syscall_x64(struct pt_regs *regs, int nr)
 	 * numbers for comparisons.
 	 */
 	unsigned int unr = nr;
+#ifdef CONFIG_ALT_SYSCALL
+	struct thread_info *ti;
+#endif
 
+#ifdef CONFIG_ALT_SYSCALL
+	ti = current_thread_info();
+	if (likely(unr < ti->nr_syscalls)) {
+		unr = array_index_nospec(unr, ti->nr_syscalls);
+		regs->ax = ti->sys_call_table[unr](regs);
+		return true;
+	}
+	return false;
+#else
 	if (likely(unr < NR_syscalls)) {
 		unr = array_index_nospec(unr, NR_syscalls);
 		regs->ax = sys_call_table[unr](regs);
 		return true;
 	}
 	return false;
+#endif
 }
 
 static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
@@ -106,13 +119,20 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs, int nr)
 	 * numbers for comparisons.
 	 */
 	unsigned int unr = nr;
-
+#ifdef CONFIG_ALT_SYSCALL
+	struct thread_info *ti = current_thread_info();
+	if (likely(unr < ti->ia32_nr_syscalls)) {
+		unr = array_index_nospec(unr, ti->ia32_nr_syscalls);
+		regs->ax = ti->ia32_sys_call_table[unr](regs);
+	}
+#else
 	if (likely(unr < IA32_NR_syscalls)) {
 		unr = array_index_nospec(unr, IA32_NR_syscalls);
 		regs->ax = ia32_sys_call_table[unr](regs);
 	} else if (nr != -1) {
 		regs->ax = __ia32_sys_ni_syscall(regs);
 	}
+#endif
 }
 
 /* Handles int $0x80 */
diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
index f7e2d82d24fb..d44258d66254 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
@@ -21,6 +21,7 @@ extern const sys_call_ptr_t sys_call_table[];
 
 #if defined(CONFIG_X86_32)
 #define ia32_sys_call_table sys_call_table
+#define ia32_nr_syscalls nr_syscalls
 #else
 /*
  * These may not exist, but still put the prototypes in so we
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index de406d93b515..b20f111c83cf 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -50,6 +50,10 @@
  */
 #ifndef __ASSEMBLY__
 struct task_struct;
+
+/* same as sys_call_ptr_t from asm/syscall.h */
+typedef asmlinkage long (*ti_sys_call_ptr_t)(const struct pt_regs *);
+
 #include <asm/cpufeature.h>
 #include <linux/atomic.h>
 
@@ -57,11 +61,42 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	unsigned long		syscall_work;	/* SYSCALL_WORK_ flags */
 	u32			status;		/* thread synchronous flags */
+#ifdef CONFIG_ALT_SYSCALL
+	/*
+	 * This uses nr_syscalls instead of nr_syscall_max because we want
+	 * to be able to entirely disable a syscall table (e.g. compat) by
+	 * setting nr_syscalls to 0. This requires some careful work in
+	 * the syscall entry assembly code, most variations use ..._max.
+	 */
+	unsigned int		nr_syscalls;	/* size of below */
+	const ti_sys_call_ptr_t	*sys_call_table;
+# ifdef CONFIG_IA32_EMULATION
+	unsigned int		ia32_nr_syscalls;	/* size of below */
+	const ti_sys_call_ptr_t	*ia32_sys_call_table;
+# endif
+#endif
 };
 
+#ifdef CONFIG_ALT_SYSCALL
+# ifdef CONFIG_IA32_EMULATION
+#  define INIT_THREAD_INFO_SYSCALL_COMPAT			\
+	.ia32_nr_syscalls	= IA32_NR_syscalls,		\
+	.ia32_sys_call_table	= ia32_sys_call_table,
+# else
+#  define INIT_THREAD_INFO_SYSCALL_COMPAT /* */
+# endif
+# define INIT_THREAD_INFO_SYSCALL \
+	.nr_syscalls	= NR_syscalls,		\
+	.sys_call_table	= sys_call_table,	\
+	INIT_THREAD_INFO_SYSCALL_COMPAT
+#else
+# define INIT_THREAD_INFO_SYSCALL /* */
+#endif
+
 #define INIT_THREAD_INFO(tsk)			\
 {						\
 	.flags		= 0,			\
+	INIT_THREAD_INFO_SYSCALL		\
 }
 
 #else /* !__ASSEMBLY__ */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 3e625c61f008..ca815f55a73b 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -150,6 +150,9 @@ obj-$(CONFIG_UNWINDER_FRAME_POINTER)	+= unwind_frame.o
 obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
 
 obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= sev.o
+
+obj-$(CONFIG_ALT_SYSCALL)		+= alt-syscall.o
+
 ###
 # 64 bit specific files
 ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/alt-syscall.c b/arch/x86/kernel/alt-syscall.c
new file mode 100644
index 000000000000..09e7ed7e3f3e
--- /dev/null
+++ b/arch/x86/kernel/alt-syscall.c
@@ -0,0 +1,70 @@
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/unistd.h>
+#include <linux/slab.h>
+#include <linux/stddef.h>
+#include <linux/syscalls.h>
+#include <linux/alt-syscall.h>
+
+#include <asm/syscall.h>
+#include <asm/syscalls.h>
+
+int arch_dup_sys_call_table(struct alt_sys_call_table *entry)
+{
+	if (!entry)
+		return -EINVAL;
+	/* Table already allocated. */
+	if (entry->table)
+		return -EINVAL;
+#ifdef CONFIG_IA32_EMULATION
+	if (entry->compat_table)
+		return -EINVAL;
+#endif
+	entry->size = NR_syscalls;
+	entry->table = kcalloc(entry->size, sizeof(sys_call_ptr_t),
+			       GFP_KERNEL);
+	if (!entry->table)
+		goto failed;
+
+	memcpy(entry->table, sys_call_table,
+	       entry->size * sizeof(sys_call_ptr_t));
+
+#ifdef CONFIG_IA32_EMULATION
+	entry->compat_size = IA32_NR_syscalls;
+	entry->compat_table = kcalloc(entry->compat_size,
+				      sizeof(sys_call_ptr_t), GFP_KERNEL);
+	if (!entry->compat_table)
+		goto failed;
+	memcpy(entry->compat_table, ia32_sys_call_table,
+	       entry->compat_size * sizeof(sys_call_ptr_t));
+#endif
+
+	return 0;
+
+failed:
+	entry->size = 0;
+	kfree(entry->table);
+	entry->table = NULL;
+#ifdef CONFIG_IA32_EMULATION
+	entry->compat_size = 0;
+#endif
+	return -ENOMEM;
+}
+
+/* Operates on "current", which isn't racey, since it's _in_ a syscall. */
+int arch_set_sys_call_table(struct alt_sys_call_table *entry)
+{
+	if (!entry)
+		return -EINVAL;
+
+	current_thread_info()->nr_syscalls = entry->size;
+	current_thread_info()->sys_call_table = entry->table;
+#ifdef CONFIG_IA32_EMULATION
+	current_thread_info()->ia32_nr_syscalls = entry->compat_size;
+	current_thread_info()->ia32_sys_call_table = entry->compat_table;
+#endif
+
+	return 0;
+}
diff --git a/security/chromiumos/Kconfig b/security/chromiumos/Kconfig
index b2afa0ef24cb..647270062c71 100644
--- a/security/chromiumos/Kconfig
+++ b/security/chromiumos/Kconfig
@@ -31,7 +31,6 @@ config SECURITY_CHROMIUMOS_NO_UNPRIVILEGED_UNSAFE_MOUNTS
 config ALT_SYSCALL_CHROMIUMOS
 	bool "Chromium OS Alt-Syscall Tables"
 	depends on ALT_SYSCALL
-	depends on X86_64 || ARM64
 	help
 	  Register restricted, alternate syscall tables used by Chromium OS
 	  using the alt-syscall infrastructure.  Alternate syscall tables
-- 
2.32.0.93.g670b81a890-goog