From 96032f983ca32ad1d43c73da922dbc7022754c3c Mon Sep 17 00:00:00 2001
From: Christophe Leroy <christophe.leroy@csgroup.eu>
Date: Tue, 7 Jul 2020 18:32:25 +0000
Subject: [PATCH] powerpc/signal64: Don't opencode page prefaulting

References: jsc#SLE-9246
Patch-mainline: v5.9-rc1
Git-commit: 96032f983ca32ad1d43c73da922dbc7022754c3c

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
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/kernel/signal_64.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 97729642f955..bfc939360bad 100644
--- 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;
 
 	/*
-- 
2.28.0