Use fault_in_pages_readable() to prefault user context
instead of open coding

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/kernel/signal_32.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 492f03451877..cfacb2726152 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c

@@ -25,6 +25,7 @@
 #include <linux/errno.h>
 #include <linux/elf.h>
 #include <linux/ptrace.h>
+#include <linux/pagemap.h>
 #include <linux/ratelimit.h>
 #ifdef CONFIG_PPC64
 #include <linux/syscalls.h>

@@ -1045,7 +1046,6 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
                     struct ucontext __user *new_ctx,
                     int ctx_size, int r6, int r7, int r8, struct pt_regs *regs)
 {
-       unsigned char tmp __maybe_unused;
        int ctx_has_vsx_region = 0;

 #ifdef CONFIG_PPC64

@@ -1109,9 +1109,8 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
        }
        if (new_ctx == NULL)
                return 0;
-       if (!access_ok(VERIFY_READ, new_ctx, ctx_size)
-           || __get_user(tmp, (u8 __user *) new_ctx)
-           || __get_user(tmp, (u8 __user *) new_ctx + ctx_size - 1))
+       if (!access_ok(VERIFY_READ, new_ctx, ctx_size) ||
+           fault_in_pages_readable((u8 __user *)new_ctx, ctx_size))
                return -EFAULT;

        /*

@@ -1231,7 +1230,6 @@ int sys_debug_setcontext(struct ucontext __user *ctx,
 {
        struct sig_dbg_op op;
        int i;
-       unsigned char tmp __maybe_unused;
        unsigned long new_msr = regs->msr;
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
        unsigned long new_dbcr0 = current->thread.debug.dbcr0;

@@ -1287,9 +1285,8 @@ int sys_debug_setcontext(struct ucontext __user *ctx,
        current->thread.debug.dbcr0 = new_dbcr0;
 #endif

-       if (!access_ok(VERIFY_READ, ctx, sizeof(*ctx))
-           || __get_user(tmp, (u8 __user *) ctx)
-           || __get_user(tmp, (u8 __user *) (ctx + 1) - 1))
+       if (!access_ok(VERIFY_READ, ctx, sizeof(*ctx)) ||
+           fault_in_pages_readable((u8 __user *)ctx, 1))