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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [PATCH v2] powerpc/signal32: Use fault_in_pages_readable() to prefault
 user context
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Mathieu Malaterre <malat@debian.org>
Message-Id: <20180424160425.DB9946C5A7@po15720vm.idsi0.si.c-s.fr>
Date:   Tue, 24 Apr 2018 18:04:25 +0200 (CEST)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 v2: using sizeof(*ctx) as size of ctx instead of 1

 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..4a9e4d6d555b 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, sizeof(*ctx)))
 		return -EFAULT;
 
 	/*
-- 
2.13.3