arm64: Provide read/write fault information in compat signal handlers

For AArch32, bit 11 (WnR) of the FSR/ESR register is set when the fault
was caused by a write access and applications like Qemu rely on such
information being provided in sigcontext. This patch introduces the
ESR_EL1 tracking for the arm64 kernel faults and sets bit 11 accordingly
in compat sigcontext.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/esr.h

@@ -18,9 +18,11 @@
 #ifndef __ASM_ESR_H
 #define __ASM_ESR_H
 
-#define ESR_EL1_EC_SHIFT	(26)
-#define ESR_EL1_IL		(1U << 25)
+#define ESR_EL1_WRITE		(1 << 6)
+#define ESR_EL1_CM		(1 << 8)
+#define ESR_EL1_IL		(1 << 25)
 
+#define ESR_EL1_EC_SHIFT	(26)
 #define ESR_EL1_EC_UNKNOWN	(0x00)
 #define ESR_EL1_EC_WFI		(0x01)
 #define ESR_EL1_EC_CP15_32	(0x03)

arch/arm64/include/asm/processor.h

@@ -79,6 +79,7 @@ struct thread_struct {
 	unsigned long		tp_value;
 	struct fpsimd_state	fpsimd_state;
 	unsigned long		fault_address;	/* fault info */
+	unsigned long		fault_code;	/* ESR_EL1 value */
 	struct debug_info	debug;		/* debugging */
 };
 

arch/arm64/kernel/signal32.c

@@ -23,6 +23,7 @@
 #include <linux/syscalls.h>
 #include <linux/ratelimit.h>
 
+#include <asm/esr.h>
 #include <asm/fpsimd.h>
 #include <asm/signal32.h>
 #include <asm/uaccess.h>
@@ -81,6 +82,8 @@ struct compat_vfp_sigframe {
 #define VFP_MAGIC		0x56465001
 #define VFP_STORAGE_SIZE	sizeof(struct compat_vfp_sigframe)
 
+#define FSR_WRITE_SHIFT		(11)
+
 struct compat_aux_sigframe {
 	struct compat_vfp_sigframe	vfp;
 
@@ -500,7 +503,9 @@ static int compat_setup_sigframe(struct compat_sigframe __user *sf,
 	__put_user_error(regs->pstate, &sf->uc.uc_mcontext.arm_cpsr, err);
 
 	__put_user_error((compat_ulong_t)0, &sf->uc.uc_mcontext.trap_no, err);
-	__put_user_error((compat_ulong_t)0, &sf->uc.uc_mcontext.error_code, err);
+	/* set the compat FSR WnR */
+	__put_user_error(!!(current->thread.fault_code & ESR_EL1_WRITE) <<
+			 FSR_WRITE_SHIFT, &sf->uc.uc_mcontext.error_code, err);
 	__put_user_error(current->thread.fault_address, &sf->uc.uc_mcontext.fault_address, err);
 	__put_user_error(set->sig[0], &sf->uc.uc_mcontext.oldmask, err);
 

arch/arm64/kernel/traps.c

@@ -251,10 +251,13 @@ void die(const char *str, struct pt_regs *regs, int err)
 void arm64_notify_die(const char *str, struct pt_regs *regs,
 		      struct siginfo *info, int err)
 {
-	if (user_mode(regs))
+	if (user_mode(regs)) {
+		current->thread.fault_address = 0;
+		current->thread.fault_code = err;
 		force_sig_info(info->si_signo, info, current);
-	else
+	} else {
 		die(str, regs, err);
+	}
 }
 
 asmlinkage void __exception do_undefinstr(struct pt_regs *regs)

arch/arm64/mm/fault.c

@@ -32,6 +32,7 @@
 
 #include <asm/exception.h>
 #include <asm/debug-monitors.h>
+#include <asm/esr.h>
 #include <asm/system_misc.h>
 #include <asm/pgtable.h>
 #include <asm/tlbflush.h>
@@ -123,6 +124,7 @@ static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 	}
 
 	tsk->thread.fault_address = addr;
+	tsk->thread.fault_code = esr;
 	si.si_signo = sig;
 	si.si_errno = 0;
 	si.si_code = code;
@@ -148,8 +150,6 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re
 #define VM_FAULT_BADMAP		0x010000
 #define VM_FAULT_BADACCESS	0x020000
 
-#define ESR_WRITE		(1 << 6)
-#define ESR_CM			(1 << 8)
 #define ESR_LNX_EXEC		(1 << 24)
 
 static int __do_page_fault(struct mm_struct *mm, unsigned long addr,
@@ -218,7 +218,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 
 	if (esr & ESR_LNX_EXEC) {
 		vm_flags = VM_EXEC;
-	} else if ((esr & ESR_WRITE) && !(esr & ESR_CM)) {
+	} else if ((esr & ESR_EL1_WRITE) && !(esr & ESR_EL1_CM)) {
 		vm_flags = VM_WRITE;
 		mm_flags |= FAULT_FLAG_WRITE;
 	}
@@ -525,7 +525,7 @@ asmlinkage int __exception do_debug_exception(unsigned long addr,
 	info.si_errno = 0;
 	info.si_code  = inf->code;
 	info.si_addr  = (void __user *)addr;
-	arm64_notify_die("", regs, &info, esr);
+	arm64_notify_die("", regs, &info, 0);
 
 	return 0;
 }