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Date:   Wed, 13 May 2020 18:00:35 +0200
From:   Christoph Hellwig <hch@....de>
To:     x86@...nel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-parisc@...r.kernel.org, linux-um@...ts.infradead.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 15/18] x86: use non-set_fs based maccess routines

Provide arch_kernel_read and arch_kernel_write routines to implement the
maccess routines without messing with set_fs and without stac/clac that
opens up access to user space.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 arch/x86/include/asm/uaccess.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index d8f283b9a569c..765e18417b3ba 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -523,5 +523,21 @@ do {									\
 	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
 } while (0)
 
+#define HAVE_ARCH_PROBE_KERNEL
+
+#define arch_kernel_read(dst, src, type, err_label)			\
+do {									\
+        int __kr_err;							\
+									\
+	__get_user_size(*((type *)dst), (__force type __user *)src,	\
+			sizeof(type), __kr_err);			\
+        if (unlikely(__kr_err))						\
+		goto err_label;						\
+} while (0)
+
+#define arch_kernel_write(dst, src, type, err_label)			\
+	__put_user_size(*((type *)(src)), (__force type __user *)(dst),	\
+			sizeof(type), err_label)
+
 #endif /* _ASM_X86_UACCESS_H */
 
-- 
2.26.2

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