diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 437dd6cf5ac8..787cee384e1c 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -152,6 +152,31 @@ config NR_CPUS depends on SMP default "4" +config SWP_EMULATE + bool "Emulate SWP/SWPB instructions" + help + ARMv6 architecture deprecates use of the SWP/SWPB instructions. ARMv8 + oblosetes the use of SWP/SWPB instructions. ARMv7 multiprocessing + extensions introduce the ability to disable these instructions, + triggering an undefined instruction exception when executed. Say Y + here to enable software emulation of these instructions for userspace + (not kernel) using LDREX/STREX. Also creates /proc/cpu/swp_emulation + for statistics. + + In some older versions of glibc [<=2.8] SWP is used during futex + trylock() operations with the assumption that the code will not + be preempted. This invalid assumption may be more likely to fail + with SWP emulation enabled, leading to deadlock of the user + application. + + NOTE: when accessing uncached shared regions, LDREX/STREX rely + on an external transaction monitoring block called a global + monitor to maintain update atomicity. If your system does not + implement a global monitor, this option can cause programs that + perform SWP operations to uncached memory to deadlock. + + If unsure, say Y. + source kernel/Kconfig.preempt config HZ @@ -185,6 +210,7 @@ config HW_PERF_EVENTS config ARMV7_COMPAT bool "Kernel support for ARMv7 applications" depends on COMPAT + select SWP_EMULATE help This option enables features that allow that ran on an ARMv7 or older processor to continue functioning. diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index d7ff1913c506..3e6706630ae5 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -18,6 +18,9 @@ arm64-obj-$(CONFIG_SMP) += smp.o smp_spin_table.o smp_psci.o arm64-obj-$(CONFIG_HW_PERF_EVENTS) += perf_event.o arm64-obj-$(CONFIG_HAVE_HW_BREAKPOINT)+= hw_breakpoint.o arm64-obj-$(CONFIG_EARLY_PRINTK) += early_printk.o +arm64-obj-$(CONFIG_ARM_CPU_SUSPEND) += sleep.o suspend.o + +obj-$(CONFIG_SWP_EMULATE) += swp_emulate.o obj-y += $(arm64-obj-y) vdso/ obj-m += $(arm64-obj-m) diff --git a/arch/arm64/kernel/swp_emulate.c b/arch/arm64/kernel/swp_emulate.c new file mode 100644 index 000000000000..05ffe59b5bc4 --- /dev/null +++ b/arch/arm64/kernel/swp_emulate.c @@ -0,0 +1,155 @@ +/* + * Derived from from linux/arch/arm/kernel/swp_emulate.c + * + * Copyright (C) 2009 ARM Limited + * Copyright (c) 2014, NVIDIA CORPORATION. All rights reserved. + * + * 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. + * + * Implements emulation of the SWP/SWPB instructions using load-exclusive and + * store-exclusive for processors that have them disabled (or future ones that + * might not implement them). + * + * Syntax of SWP{B} instruction: SWP{B} , , [] + * Where: Rt = destination + * Rt2 = source + * Rn = address + */ + +#include +#include +#include +#include +#include +#include +#include + +#include +#include +#include +#include +#include + +/* + * Macros/defines for extracting register numbers from instruction. + */ +#define EXTRACT_REG_NUM(instruction, offset) \ + (((instruction) & (0xf << (offset))) >> (offset)) +#define RN_OFFSET 16 +#define RT_OFFSET 12 +#define RT2_OFFSET 0 +/* + * Bit 22 of the instruction encoding distinguishes between + * the SWP and SWPB variants (bit set means SWPB). + */ +#define TYPE_SWPB (1 << 22) + +static pid_t previous_pid; + +u64 swpb_count = 0; +u64 swp_count = 0; + +/* + * swp_handler logs the id of calling process, dissects the instruction, sanity + * checks the memory location, calls emulate_swpX for the actual operation and + * deals with fixup/error handling before returning + */ +static int swp_handler(struct pt_regs *regs, unsigned int instr) +{ + u32 address_reg, destreg, data, type; + uintptr_t address; + unsigned int res = 0; + u32 temp32; + u8 temp8; + + perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->pc); + + res = arm_check_condition(instr, regs->pstate); + switch (res) { + case ARM_OPCODE_CONDTEST_PASS: + break; + case ARM_OPCODE_CONDTEST_FAIL: + /* Condition failed - return to next instruction */ + regs->pc += 4; + return 0; + case ARM_OPCODE_CONDTEST_UNCOND: + /* If unconditional encoding - not a SWP, undef */ + return -EFAULT; + default: + return -EINVAL; + } + + if (current->pid != previous_pid) { + pr_warn("\"%s\" (%ld) uses obsolete SWP{B} instruction\n", + current->comm, (unsigned long)current->pid); + previous_pid = current->pid; + } + + address = regs->regs[EXTRACT_REG_NUM(instr, RN_OFFSET)] & 0xffffffff; + data = regs->regs[EXTRACT_REG_NUM(instr, RT2_OFFSET)]; + destreg = EXTRACT_REG_NUM(instr, RT_OFFSET); + + type = instr & TYPE_SWPB; + + /* Check access in reasonable access range for both SWP and SWPB */ + if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) { + pr_debug("SWP{B} emulation: access to %p not allowed!\n", + (void *)address); + res = -EFAULT; + } + if (type == TYPE_SWPB) { + do { + temp8 = ldax8((u8 *) address); + } while (stx8((u8 *) address, (u8) data)); + regs->regs[destreg] = temp8; + regs->pc += 4; + swpb_count++; + } else if (address & 0x3) { + /* SWP to unaligned address not permitted */ + pr_debug("SWP instruction on unaligned pointer!\n"); + return -EFAULT; + } else { + do { + temp32 = ldax32((u32 *) address); + } while (stlx32((u32 *) address, (u32) data)); + regs->regs[destreg] = temp32; + regs->pc += 4; + swp_count++; + } + + return 0; +} + +/* + * Only emulate SWP/SWPB executed in ARM state/User mode. + * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE. + */ +static struct undef_hook swp_hook = { + .instr_mask = 0x0fb00ff0, + .instr_val = 0x01000090, + .pstate_mask = COMPAT_PSR_MODE_MASK | COMPAT_PSR_T_BIT, + .pstate_val = COMPAT_PSR_MODE_USR, + .fn = swp_handler +}; + +/* + * Register handler and create status file in /proc/cpu + * Invoked as late_initcall, since not needed before init spawned. + */ +static int __init swp_emulation_init(void) +{ + struct dentry *dir; + dir = debugfs_create_dir("swp_emulate", NULL); + debugfs_create_u64("swp_count", S_IRUGO | S_IWUSR, dir, &swp_count); + debugfs_create_u64("swpb_count", S_IRUGO | S_IWUSR, dir, &swpb_count); + + pr_notice("Registering SWP/SWPB emulation handler\n"); + register_undef_hook(&swp_hook); + + + return 0; +} + +late_initcall(swp_emulation_init);