[PATCH] ARM: tls: context switch user writeable TLS registerTPIDRURW
From: Jonathan Austin
Date: Fri Feb 08 2013 - 10:55:12 EST
Since commit 6a1c53124aa1 ("ARM: 7403/1: tls: remove covert channel via
TPIDRURW") we have zeroed the user writeable TLS register to prevent it
from being used as a covert channel between two tasks.
However, it turns out that the wine guys would rather we actually
switched the register so that WinRT applications can use it to store a
pointer to their `thread environment block (TEB)'.
This patch implements TPIDRURW context-switching for cpus implementing
the register. Unlike the TPIDRURO, which is already switched, the TPIDRURW
can be updated from userspace so needs careful treatment in the case that we
modify TPIDRURW and call fork(). If no context switch occurs between these
two events then the thread_info struct that we use to construct the child
will have the old, stale, TPIDRURW value. To avoid this we must always read
TPIDRURW in copy_thread.
This patch is extended from an earlier version by Will Deacon in order to:
- Save TPIDRURW at context switch
- Deal with the race condition described above, including adding C-getters
Reported-by: Andre Hentschel <nerv@xxxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Jonathan Austin <jonathan.austin@xxxxxxx>
---
arch/arm/include/asm/thread_info.h | 2 +-
arch/arm/include/asm/tls.h | 51 +++++++++++++++++++++++++++++-------
arch/arm/kernel/Makefile | 2 +-
arch/arm/kernel/entry-armv.S | 5 +++-
arch/arm/kernel/process.c | 4 ++-
arch/arm/kernel/ptrace.c | 2 +-
arch/arm/kernel/tls.c | 50 +++++++++++++++++++++++++++++++++++
arch/arm/kernel/traps.c | 4 +--
8 files changed, 104 insertions(+), 16 deletions(-)
create mode 100644 arch/arm/kernel/tls.c
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index cddda1f..d90be6d 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -58,7 +58,7 @@ struct thread_info {
struct cpu_context_save cpu_context; /* cpu context */
__u32 syscall; /* syscall number */
__u8 used_cp[16]; /* thread used copro */
- unsigned long tp_value;
+ unsigned long tp_value[2]; /* TLS registers */
#ifdef CONFIG_CRUNCH
struct crunch_state crunchstate;
#endif
diff --git a/arch/arm/include/asm/tls.h b/arch/arm/include/asm/tls.h
index 73409e6..e292794 100644
--- a/arch/arm/include/asm/tls.h
+++ b/arch/arm/include/asm/tls.h
@@ -5,10 +5,19 @@
.macro set_tls_none, tp, tmp1, tmp2
.endm
+ .macro save_tlsuser_none, tp, tmp1, tmp2
+ .endm
+
.macro set_tls_v6k, tp, tmp1, tmp2
- mcr p15, 0, \tp, c13, c0, 3 @ set TLS register
- mov \tmp1, #0
- mcr p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register
+ ldrd \tmp1, \tmp2, [\tp]
+ mcr p15, 0, \tmp1, c13, c0, 3 @ set user r/o TLS register
+ mcr p15, 0, \tmp2, c13, c0, 2 @ set user r/w TLS register
+ .endm
+
+ .macro save_tlsuser_v6k, tp, tmp1, tmp2
+ @ TPIDRURW can be updated from userspace, so we have to re-read it
+ mrc p15, 0, \tmp2, c13, c0, 2 @ load user r/w TLS register
+ str \tmp2, [\tp, #4]
.endm
.macro set_tls_v6, tp, tmp1, tmp2
@@ -16,15 +25,26 @@
ldr \tmp1, [\tmp1, #0]
mov \tmp2, #0xffff0fff
tst \tmp1, #HWCAP_TLS @ hardware TLS available?
- mcrne p15, 0, \tp, c13, c0, 3 @ yes, set TLS register
- movne \tmp1, #0
- mcrne p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register
- streq \tp, [\tmp2, #-15] @ set TLS value at 0xffff0ff0
+ ldrned \tmp1, \tmp2, [\tp]
+ ldreq \tmp1, [\tp]
+ mcrne p15, 0, \tmp1, c13, c0, 3 @ yes, set user r/o TLS register
+ mcrne p15, 0, \tmp2, c13, c0, 2 @ set user r/w TLS register
+ streq \tmp1, [\tmp2, #-15] @ set TLS value at 0xffff0ff0
+ .endm
+
+ .macro save_tlsuser_v6, tp, tmp1, tmp2
+ @ TPIDRURW can be updated from userspace, so we have to re-read it
+ ldr \tmp1, =elf_hwcap
+ ldr \tmp1, [\tmp1, #0]
+ tst \tmp1, #HWCAP_TLS @ hardware TLS available?
+ mrcne p15, 0, \tmp2, c13, c0, 2 @ read user r/w TLS register
+ strne \tmp2, [\tp, #4] @ save in to thread_info
.endm
.macro set_tls_software, tp, tmp1, tmp2
- mov \tmp1, #0xffff0fff
- str \tp, [\tmp1, #-15] @ set TLS value at 0xffff0ff0
+ ldr \tmp1, [\tp]
+ mov \tmp2, #0xffff0fff
+ str \tmp1, [\tmp2, #-15] @ set TLS value at 0xffff0ff0
.endm
#endif
@@ -32,18 +52,31 @@
#define tls_emu 1
#define has_tls_reg 1
#define set_tls set_tls_none
+#define save_tlsuser save_tlsuser_none
+#define get_tlsuser get_tlsuser_none
#elif defined(CONFIG_CPU_V6)
#define tls_emu 0
#define has_tls_reg (elf_hwcap & HWCAP_TLS)
#define set_tls set_tls_v6
+#define save_tlsuser save_tlsuser_v6
+#define get_tlsuser get_tlsuser_v6
#elif defined(CONFIG_CPU_32v6K)
#define tls_emu 0
#define has_tls_reg 1
#define set_tls set_tls_v6k
+#define save_tlsuser save_tlsuser_v6k
+#define get_tlsuser get_tlsuser_v6k
#else
#define tls_emu 0
#define has_tls_reg 0
#define set_tls set_tls_software
+#define save_tlsuser save_tlsuser_none
+#define get_tlsuser get_tlsuser_none
#endif
+#ifndef __ASSEMBLY__
+extern unsigned long get_tlsuser_none(void);
+extern unsigned long get_tlsuser_v6(void);
+extern unsigned long get_tlsuser_v6k(void);
+#endif
#endif /* __ASMARM_TLS_H */
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 5f3338e..4e1114c 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -17,7 +17,7 @@ CFLAGS_REMOVE_return_address.o = -pg
obj-y := elf.o entry-armv.o entry-common.o irq.o opcodes.o \
process.o ptrace.o return_address.o sched_clock.o \
- setup.o signal.o stacktrace.o sys_arm.o time.o traps.o
+ setup.o signal.o stacktrace.o sys_arm.o time.o tls.o traps.o
obj-$(CONFIG_ATAGS) += atags_parse.o
obj-$(CONFIG_ATAGS_PROC) += atags_proc.o
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 0f82098..66adb0c 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -728,7 +728,7 @@ ENTRY(__switch_to)
UNWIND(.fnstart )
UNWIND(.cantunwind )
add ip, r1, #TI_CPU_SAVE
- ldr r3, [r2, #TI_TP_VALUE]
+ add r3, r1, #TI_TP_VALUE
ARM( stmia ip!, {r4 - sl, fp, sp, lr} ) @ Store most regs on stack
THUMB( stmia ip!, {r4 - sl, fp} ) @ Store most regs on stack
THUMB( str sp, [ip], #4 )
@@ -736,6 +736,9 @@ ENTRY(__switch_to)
#ifdef CONFIG_CPU_USE_DOMAINS
ldr r6, [r2, #TI_CPU_DOMAIN]
#endif
+ /* Save the user-writeable tls register */
+ save_tlsuser r3, r4, r5
+ add r3, r2, #TI_TP_VALUE
set_tls r3, r4, r5
#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
ldr r7, [r2, #TI_TASK]
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 047d3e4..24dbc72 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -39,6 +39,7 @@
#include <asm/thread_notify.h>
#include <asm/stacktrace.h>
#include <asm/mach/time.h>
+#include <asm/tls.h>
#ifdef CONFIG_CC_STACKPROTECTOR
#include <linux/stackprotector.h>
@@ -395,7 +396,8 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start,
clear_ptrace_hw_breakpoint(p);
if (clone_flags & CLONE_SETTLS)
- thread->tp_value = childregs->ARM_r3;
+ thread->tp_value[0] = childregs->ARM_r3;
+ thread->tp_value[1] = get_tlsuser();
thread_notify(THREAD_NOTIFY_COPY, thread);
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 03deeff..2bc1514 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -849,7 +849,7 @@ long arch_ptrace(struct task_struct *child, long request,
#endif
case PTRACE_GET_THREAD_AREA:
- ret = put_user(task_thread_info(child)->tp_value,
+ ret = put_user(task_thread_info(child)->tp_value[0],
datap);
break;
diff --git a/arch/arm/kernel/tls.c b/arch/arm/kernel/tls.c
new file mode 100644
index 0000000..1627f5b
--- /dev/null
+++ b/arch/arm/kernel/tls.c
@@ -0,0 +1,50 @@
+/*
+ * arch/arm/kernel/tls.c
+ *
+ * Copyright (C) 2013 ARM Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <linux/kernel.h>
+#include <asm/tls.h>
+
+/*
+ * Access to the TPIDRURW register, with full certainty that it exists.
+ */
+unsigned long get_tlsuser_v6k(void)
+{
+ unsigned long v;
+ asm("mrc p15, 0, %0, c13, c0, 2\n" : "=r" (v));
+ return v;
+}
+
+/*
+ * Access to the TPIDRURW register if it exists.
+ */
+unsigned long get_tlsuser_v6(void)
+{
+ unsigned long v = 0;
+ if (elf_hwcap & HWCAP_TLS)
+ asm("mrc p15, 0, %0, c13, c0, 2\n" : "=r" (v));
+ return v;
+}
+
+/*
+ * Dummy access for the case that TLS is emulated in software
+ */
+unsigned long get_tlsuser_none(void)
+{
+ return 0;
+}
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 1c08911..f9d6259 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -588,7 +588,7 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
return regs->ARM_r0;
case NR(set_tls):
- thread->tp_value = regs->ARM_r0;
+ thread->tp_value[0] = regs->ARM_r0;
if (tls_emu)
return 0;
if (has_tls_reg) {
@@ -706,7 +706,7 @@ static int get_tp_trap(struct pt_regs *regs, unsigned int instr)
int reg = (instr >> 12) & 15;
if (reg == 15)
return 1;
- regs->uregs[reg] = current_thread_info()->tp_value;
+ regs->uregs[reg] = current_thread_info()->tp_value[0];
regs->ARM_pc += 4;
return 0;
}
--
1.7.9.5
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