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Diffstat (limited to 'arch/arm/kernel/swp_emulate.c')
| -rw-r--r-- | arch/arm/kernel/swp_emulate.c | 259 |
1 files changed, 259 insertions, 0 deletions
diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c new file mode 100644 index 0000000000..fdce83c95a --- /dev/null +++ b/arch/arm/kernel/swp_emulate.c @@ -0,0 +1,259 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * linux/arch/arm/kernel/swp_emulate.c + * + * Copyright (C) 2009 ARM Limited + * __user_* functions adapted from include/asm/uaccess.h + * + * 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}<c> <Rt>, <Rt2>, [<Rn>] + * Where: Rt = destination + * Rt2 = source + * Rn = address + */ + +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/proc_fs.h> +#include <linux/seq_file.h> +#include <linux/sched.h> +#include <linux/sched/mm.h> +#include <linux/syscalls.h> +#include <linux/perf_event.h> + +#include <asm/opcodes.h> +#include <asm/system_info.h> +#include <asm/traps.h> +#include <linux/uaccess.h> + +/* + * Error-checking SWP macros implemented using ldrex{b}/strex{b} + */ +#define __user_swpX_asm(data, addr, res, temp, B) \ + __asm__ __volatile__( \ + ".arch armv7-a\n" \ + "0: ldrex"B" %2, [%3]\n" \ + "1: strex"B" %0, %1, [%3]\n" \ + " cmp %0, #0\n" \ + " moveq %1, %2\n" \ + " movne %0, %4\n" \ + "2:\n" \ + " .section .text.fixup,\"ax\"\n" \ + " .align 2\n" \ + "3: mov %0, %5\n" \ + " b 2b\n" \ + " .previous\n" \ + " .section __ex_table,\"a\"\n" \ + " .align 3\n" \ + " .long 0b, 3b\n" \ + " .long 1b, 3b\n" \ + " .previous" \ + : "=&r" (res), "+r" (data), "=&r" (temp) \ + : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \ + : "cc", "memory") + +#define __user_swp_asm(data, addr, res, temp) \ + __user_swpX_asm(data, addr, res, temp, "") +#define __user_swpb_asm(data, addr, res, temp) \ + __user_swpX_asm(data, addr, res, temp, "b") + +/* + * 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 unsigned long swpcounter; +static unsigned long swpbcounter; +static unsigned long abtcounter; +static pid_t previous_pid; + +#ifdef CONFIG_PROC_FS +static int proc_status_show(struct seq_file *m, void *v) +{ + seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter); + seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter); + seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter); + if (previous_pid != 0) + seq_printf(m, "Last process:\t\t%d\n", previous_pid); + return 0; +} +#endif + +/* + * Set up process info to signal segmentation fault - called on access error. + */ +static void set_segfault(struct pt_regs *regs, unsigned long addr) +{ + int si_code; + + mmap_read_lock(current->mm); + if (find_vma(current->mm, addr) == NULL) + si_code = SEGV_MAPERR; + else + si_code = SEGV_ACCERR; + mmap_read_unlock(current->mm); + + pr_debug("SWP{B} emulation: access caused memory abort!\n"); + arm_notify_die("Illegal memory access", regs, + SIGSEGV, si_code, + (void __user *)instruction_pointer(regs), + 0, 0); + + abtcounter++; +} + +static int emulate_swpX(unsigned int address, unsigned int *data, + unsigned int type) +{ + unsigned int res = 0; + + if ((type != TYPE_SWPB) && (address & 0x3)) { + /* SWP to unaligned address not permitted */ + pr_debug("SWP instruction on unaligned pointer!\n"); + return -EFAULT; + } + + while (1) { + unsigned long temp; + unsigned int __ua_flags; + + __ua_flags = uaccess_save_and_enable(); + if (type == TYPE_SWPB) + __user_swpb_asm(*data, address, res, temp); + else + __user_swp_asm(*data, address, res, temp); + uaccess_restore(__ua_flags); + + if (likely(res != -EAGAIN) || signal_pending(current)) + break; + + cond_resched(); + } + + if (res == 0) { + if (type == TYPE_SWPB) + swpbcounter++; + else + swpcounter++; + } + + return res; +} + +/* + * 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) +{ + unsigned int address, destreg, data, type; + unsigned int res = 0; + + perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc); + + res = arm_check_condition(instr, regs->ARM_cpsr); + switch (res) { + case ARM_OPCODE_CONDTEST_PASS: + break; + case ARM_OPCODE_CONDTEST_FAIL: + /* Condition failed - return to next instruction */ + regs->ARM_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_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n", + current->comm, (unsigned long)current->pid); + previous_pid = current->pid; + } + + address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)]; + data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)]; + destreg = EXTRACT_REG_NUM(instr, RT_OFFSET); + + type = instr & TYPE_SWPB; + + pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n", + EXTRACT_REG_NUM(instr, RN_OFFSET), address, + destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data); + + /* Check access in reasonable access range for both SWP and SWPB */ + if (!access_ok((void __user *)(address & ~3), 4)) { + pr_debug("SWP{B} emulation: access to %p not allowed!\n", + (void *)address); + res = -EFAULT; + } else { + res = emulate_swpX(address, &data, type); + } + + if (res == 0) { + /* + * On successful emulation, revert the adjustment to the PC + * made in kernel/traps.c in order to resume execution at the + * instruction following the SWP{B}. + */ + regs->ARM_pc += 4; + regs->uregs[destreg] = data; + } else if (res == -EFAULT) { + /* + * Memory errors do not mean emulation failed. + * Set up signal info to return SEGV, then return OK + */ + set_segfault(regs, address); + } + + 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, + .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT, + .cpsr_val = USR_MODE, + .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) +{ + if (cpu_architecture() < CPU_ARCH_ARMv7) + return 0; + +#ifdef CONFIG_PROC_FS + if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL, + proc_status_show)) + return -ENOMEM; +#endif /* CONFIG_PROC_FS */ + + pr_notice("Registering SWP/SWPB emulation handler\n"); + register_undef_hook(&swp_hook); + + return 0; +} + +late_initcall(swp_emulation_init); |