diff --git a/Documentation/arm64/legacy_instructions.txt b/Documentation/arm64/legacy_instructions.txt
index 49d4867c0c09e5603031384ad96ecb899a576378..5ab58614b7eddf75e5e9119d11fa4a80d0b73609 100644
--- a/Documentation/arm64/legacy_instructions.txt
+++ b/Documentation/arm64/legacy_instructions.txt
@@ -31,3 +31,10 @@ behaviours and the corresponding values of the sysctl nodes -
The default mode depends on the status of the instruction in the
architecture. Deprecated instructions should default to emulation
while obsolete instructions must be undefined by default.
+
+Supported legacy instructions
+-----------------------------
+* SWP{B}
+Node: /proc/sys/abi/swp
+Status: Obsolete
+Default: Undef (0)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index aa8f4bea373869d878e72ba9eb4aceab365b026f..2b6213840ec86e2138e6a9a6bd3f1b603e991a1e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -180,6 +180,27 @@ menuconfig ARMV8_DEPRECATED
if ARMV8_DEPRECATED
+config SWP_EMULATION
+ bool "Emulate SWP/SWPB instructions"
+ help
+ ARMv8 obsoletes the use of A32 SWP/SWPB instructions such that
+ they are always undefined. Say Y here to enable software
+ emulation of these instructions for userspace using LDXR/STXR.
+
+ 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, LDXR/STXR 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
+
endif
endmenu
diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index 1bb043018315c53857d2a35c94d98c486d5db08f..3ecc57c47c04ee9d5ccd03e98af8ae920a816efc 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -356,6 +356,12 @@ int aarch64_insn_patch_text_sync(void *addrs[], u32 insns[], int cnt);
int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
bool aarch32_insn_is_wide(u32 insn);
+
+#define A32_RN_OFFSET 16
+#define A32_RT_OFFSET 12
+#define A32_RT2_OFFSET 0
+
+u32 aarch32_insn_extract_reg_num(u32 insn, int offset);
#endif /* __ASSEMBLY__ */
#endif /* __ASM_INSN_H */
diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
index db3b79da6a4809773f9f41bde35fd31ff285abcc..98865a7868f18fd2efb6c105501b384e2434dfc0 100644
--- a/arch/arm64/kernel/armv8_deprecated.c
+++ b/arch/arm64/kernel/armv8_deprecated.c
@@ -8,10 +8,16 @@
#include <linux/init.h>
#include <linux/list.h>
+#include <linux/perf_event.h>
+#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/sysctl.h>
+#include <asm/insn.h>
+#include <asm/opcodes.h>
+#include <asm/system_misc.h>
#include <asm/traps.h>
+#include <asm/uaccess.h>
/*
* The runtime support for deprecated instruction support can be in one of
@@ -203,11 +209,196 @@ static void register_insn_emulation_sysctl(struct ctl_table *table)
register_sysctl_table(table);
}
+/*
+ * Implement emulation of the SWP/SWPB instructions using load-exclusive and
+ * store-exclusive.
+ *
+ * Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
+ * Where: Rt = destination
+ * Rt2 = source
+ * Rn = address
+ */
+
+/*
+ * Error-checking SWP macros implemented using ldxr{b}/stxr{b}
+ */
+#define __user_swpX_asm(data, addr, res, temp, B) \
+ __asm__ __volatile__( \
+ " mov %w2, %w1\n" \
+ "0: ldxr"B" %w1, [%3]\n" \
+ "1: stxr"B" %w0, %w2, [%3]\n" \
+ " cbz %w0, 2f\n" \
+ " mov %w0, %w4\n" \
+ "2:\n" \
+ " .pushsection .fixup,\"ax\"\n" \
+ " .align 2\n" \
+ "3: mov %w0, %w5\n" \
+ " b 2b\n" \
+ " .popsection" \
+ " .pushsection __ex_table,\"a\"\n" \
+ " .align 3\n" \
+ " .quad 0b, 3b\n" \
+ " .quad 1b, 3b\n" \
+ " .popsection" \
+ : "=&r" (res), "+r" (data), "=&r" (temp) \
+ : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
+ : "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")
+
+/*
+ * Bit 22 of the instruction encoding distinguishes between
+ * the SWP and SWPB variants (bit set means SWPB).
+ */
+#define TYPE_SWPB (1 << 22)
+
+/*
+ * Set up process info to signal segmentation fault - called on access error.
+ */
+static void set_segfault(struct pt_regs *regs, unsigned long addr)
+{
+ siginfo_t info;
+
+ down_read(¤t->mm->mmap_sem);
+ if (find_vma(current->mm, addr) == NULL)
+ info.si_code = SEGV_MAPERR;
+ else
+ info.si_code = SEGV_ACCERR;
+ up_read(¤t->mm->mmap_sem);
+
+ info.si_signo = SIGSEGV;
+ info.si_errno = 0;
+ info.si_addr = (void *) instruction_pointer(regs);
+
+ pr_debug("SWP{B} emulation: access caused memory abort!\n");
+ arm64_notify_die("Illegal memory access", regs, &info, 0);
+}
+
+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;
+
+ if (type == TYPE_SWPB)
+ __user_swpb_asm(*data, address, res, temp);
+ else
+ __user_swp_asm(*data, address, res, temp);
+
+ if (likely(res != -EAGAIN) || signal_pending(current))
+ break;
+
+ cond_resched();
+ }
+
+ 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, u32 instr)
+{
+ u32 destreg, data, type, address = 0;
+ int rn, rt2, res = 0;
+
+ perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->pc);
+
+ type = instr & TYPE_SWPB;
+
+ switch (arm_check_condition(instr, regs->pstate)) {
+ case ARM_OPCODE_CONDTEST_PASS:
+ break;
+ case ARM_OPCODE_CONDTEST_FAIL:
+ /* Condition failed - return to next instruction */
+ goto ret;
+ case ARM_OPCODE_CONDTEST_UNCOND:
+ /* If unconditional encoding - not a SWP, undef */
+ return -EFAULT;
+ default:
+ return -EINVAL;
+ }
+
+ rn = aarch32_insn_extract_reg_num(instr, A32_RN_OFFSET);
+ rt2 = aarch32_insn_extract_reg_num(instr, A32_RT2_OFFSET);
+
+ address = (u32)regs->user_regs.regs[rn];
+ data = (u32)regs->user_regs.regs[rt2];
+ destreg = aarch32_insn_extract_reg_num(instr, A32_RT_OFFSET);
+
+ pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
+ rn, address, destreg,
+ aarch32_insn_extract_reg_num(instr, A32_RT2_OFFSET), data);
+
+ /* 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 0x%08x not allowed!\n",
+ address);
+ goto fault;
+ }
+
+ res = emulate_swpX(address, &data, type);
+ if (res == -EFAULT)
+ goto fault;
+ else if (res == 0)
+ regs->user_regs.regs[destreg] = data;
+
+ret:
+ pr_warn_ratelimited("\"%s\" (%ld) uses obsolete SWP{B} instruction at 0x%llx\n",
+ current->comm, (unsigned long)current->pid, regs->pc);
+
+ regs->pc += 4;
+ return 0;
+
+fault:
+ 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.
+ */
+static struct undef_hook swp_hooks[] = {
+ {
+ .instr_mask = 0x0fb00ff0,
+ .instr_val = 0x01000090,
+ .pstate_mask = COMPAT_PSR_MODE_MASK,
+ .pstate_val = COMPAT_PSR_MODE_USR,
+ .fn = swp_handler
+ },
+ { }
+};
+
+static struct insn_emulation_ops swp_ops = {
+ .name = "swp",
+ .status = INSN_OBSOLETE,
+ .hooks = swp_hooks,
+ .set_hw_mode = NULL,
+};
+
/*
* Invoked as late_initcall, since not needed before init spawned.
*/
static int __init armv8_deprecated_init(void)
{
+ if (IS_ENABLED(CONFIG_SWP_EMULATION))
+ register_insn_emulation(&swp_ops);
+
register_insn_emulation_sysctl(ctl_abi);
return 0;
diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index ab00eb58d3857c27708c0566e2fccd197d201265..63122dcd8524d2122984a032bbe4946e6769da67 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -964,3 +964,11 @@ bool aarch32_insn_is_wide(u32 insn)
{
return insn >= 0xe800;
}
+
+/*
+ * Macros/defines for extracting register numbers from instruction.
+ */
+u32 aarch32_insn_extract_reg_num(u32 insn, int offset)
+{
+ return (insn & (0xf << offset)) >> offset;
+}