powerpc/signal64: Don't opencode page prefaulting

Instead of doing a __get_user() from the first and last location
into a tmp var which won't be used, use fault_in_pages_readable()

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/810bd8840ef990a200f58c9dea9abe767ca02a3a.1594146723.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 97729642f9556a9e2984dd996079d999e4bf3b3f..bfc939360bad3afd28cd8d04abde7df0da79bd08 100644 (file)
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -21,6 +21,7 @@
 #include <linux/ptrace.h>
 #include <linux/ratelimit.h>
 #include <linux/syscalls.h>
+#include <linux/pagemap.h>
 
 #include <asm/sigcontext.h>
 #include <asm/ucontext.h>
@@ -634,7 +635,6 @@ static long setup_trampoline(unsigned int syscall, unsigned int __user *tramp)
 SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
                struct ucontext __user *, new_ctx, long, ctx_size)
 {
-       unsigned char tmp;
        sigset_t set;
        unsigned long new_msr = 0;
        int ctx_has_vsx_region = 0;
@@ -669,9 +669,8 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
        }
        if (new_ctx == NULL)
                return 0;
-       if (!access_ok(new_ctx, ctx_size)
-           || __get_user(tmp, (u8 __user *) new_ctx)
-           || __get_user(tmp, (u8 __user *) new_ctx + ctx_size - 1))
+       if (!access_ok(new_ctx, ctx_size) ||
+           fault_in_pages_readable((u8 __user *)new_ctx, ctx_size))
                return -EFAULT;
 
        /*