arm64: compat: Check for AArch32 state

Make sure we have AArch32 state available for running COMPAT
binaries and also for switching the personality to PER_LINUX32.
Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
[ Added cap bit, checks for HWCAP, personality ]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Tested-by: Yury Norov <ynorov@caviumnetworks.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/elf.h

@@ -177,7 +177,8 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
 
 /* AArch32 EABI. */
 #define EF_ARM_EABI_MASK		0xff000000
-#define compat_elf_check_arch(x)	(((x)->e_machine == EM_ARM) && \
+#define compat_elf_check_arch(x)	(system_supports_32bit_el0() && \
+					 ((x)->e_machine == EM_ARM) && \
 					 ((x)->e_flags & EF_ARM_EABI_MASK))
 
 #define compat_start_thread		compat_start_thread

arch/arm64/kernel/cpufeature.c

@@ -987,6 +987,7 @@ void verify_local_cpu_capabilities(void)
 
 	verify_local_cpu_features(arm64_features);
 	verify_local_elf_hwcaps(arm64_elf_hwcaps);
+	if (system_supports_32bit_el0())
 		verify_local_elf_hwcaps(compat_elf_hwcaps);
 }
 
@@ -1004,6 +1005,8 @@ void __init setup_cpu_features(void)
 	/* Set the CPU feature capabilies */
 	setup_feature_capabilities();
 	setup_elf_hwcaps(arm64_elf_hwcaps);
+
+	if (system_supports_32bit_el0())
 		setup_elf_hwcaps(compat_elf_hwcaps);
 
 	/* Advertise that we have computed the system capabilities */

arch/arm64/kernel/sys.c

@@ -25,6 +25,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/syscalls.h>
+#include <asm/cpufeature.h>
 
 asmlinkage long sys_mmap(unsigned long addr, unsigned long len,
 			 unsigned long prot, unsigned long flags,
@@ -36,11 +37,20 @@ asmlinkage long sys_mmap(unsigned long addr, unsigned long len,
 	return sys_mmap_pgoff(addr, len, prot, flags, fd, off >> PAGE_SHIFT);
 }
 
+SYSCALL_DEFINE1(arm64_personality, unsigned int, personality)
+{
+	if (personality(personality) == PER_LINUX32 &&
+		!system_supports_32bit_el0())
+		return -EINVAL;
+	return sys_personality(personality);
+}
+
 /*
  * Wrappers to pass the pt_regs argument.
  */
 asmlinkage long sys_rt_sigreturn_wrapper(void);
 #define sys_rt_sigreturn	sys_rt_sigreturn_wrapper
+#define sys_personality		sys_arm64_personality
 
 #undef __SYSCALL
 #define __SYSCALL(nr, sym)	[nr] = sym,