linux-kernel - Re: [PATCH v4 5/6] add listmount(2) syscall

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Message-Id: <07d8877b-d933-46f4-8ca4-c10ed602f37e@app.fastmail.com>
Date: Fri, 12 Jan 2024 00:01:34 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Linus Torvalds" <torvalds@...ux-foundation.org>,
 "Guenter Roeck" <linux@...ck-us.net>,
 "Yoshinori Sato" <ysato@...rs.sourceforge.jp>,
 "Rich Felker" <dalias@...c.org>,
 "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.de>
Cc: "Miklos Szeredi" <mszeredi@...hat.com>, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
 linux-man@...r.kernel.org, linux-security-module@...r.kernel.org,
 "Karel Zak" <kzak@...hat.com>, "Ian Kent" <raven@...maw.net>,
 "David Howells" <dhowells@...hat.com>,
 "Alexander Viro" <viro@...iv.linux.org.uk>,
 "Christian Brauner" <christian@...uner.io>,
 "Amir Goldstein" <amir73il@...il.com>,
 "Matthew House" <mattlloydhouse@...il.com>,
 "Florian Weimer" <fweimer@...hat.com>
Subject: Re: [PATCH v4 5/6] add listmount(2) syscall

On Thu, Jan 11, 2024, at 21:14, Linus Torvalds wrote:

> The SH put_user64() needs to be looked at too, but in the meantime,
> maybe something like this fixes the problems with listmount?

I tried changing it to use the generic memcpy() based uaccess
that m68k-nommu and riscv-nommu use, which also avoids the
build failure. I still run into other unrelated build issues
on arch/sh, so I'm not sure if this is a sufficient fix.

     Arnd

diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 7500521b2b98..2cc3a541e231 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -73,6 +73,7 @@ config SUPERH
        select PERF_USE_VMALLOC
        select RTC_LIB
        select SPARSE_IRQ
+       select UACCESS_MEMCPY if !MMU
        select TRACE_IRQFLAGS_SUPPORT
        help
          The SuperH is a RISC processor targeted for use in embedded systems
diff --git a/arch/sh/include/asm/uaccess.h b/arch/sh/include/asm/uaccess.h
index a79609eb14be..b42764d55901 100644
--- a/arch/sh/include/asm/uaccess.h
+++ b/arch/sh/include/asm/uaccess.h
@@ -2,6 +2,7 @@
 #ifndef __ASM_SH_UACCESS_H
 #define __ASM_SH_UACCESS_H
 
+#ifdef CONFIG_MMU
 #include <asm/extable.h>
 #include <asm-generic/access_ok.h>
 
@@ -130,4 +131,8 @@ struct mem_access {
 int handle_unaligned_access(insn_size_t instruction, struct pt_regs *regs,
                            struct mem_access *ma, int, unsigned long address);
 
+#else
+#include <asm-generic/uaccess.h>
+#endif
+
 #endif /* __ASM_SH_UACCESS_H */
diff --git a/arch/sh/include/asm/uaccess_32.h b/arch/sh/include/asm/uaccess_32.h
index 5d7ddc092afd..e053f2fd245c 100644
--- a/arch/sh/include/asm/uaccess_32.h
+++ b/arch/sh/include/asm/uaccess_32.h
@@ -35,7 +35,6 @@ do {                                                          \
        }                                                       \
 } while (0)
 
-#ifdef CONFIG_MMU
 #define __get_user_asm(x, addr, err, insn) \
 ({ \
 __asm__ __volatile__( \
@@ -56,16 +55,6 @@ __asm__ __volatile__( \
        ".previous" \
        :"=&r" (err), "=&r" (x) \
        :"m" (__m(addr)), "i" (-EFAULT), "0" (err)); })
-#else
-#define __get_user_asm(x, addr, err, insn)             \
-do {                                                   \
-       __asm__ __volatile__ (                          \
-               "mov." insn "   %1, %0\n\t"             \
-               : "=&r" (x)                             \
-               : "m" (__m(addr))                       \
-       );                                              \
-} while (0)
-#endif /* CONFIG_MMU */
 
 extern void __get_user_unknown(void);
 
@@ -140,7 +129,6 @@ do {                                                        \
        }                                               \
 } while (0)
 
-#ifdef CONFIG_MMU
 #define __put_user_asm(x, addr, err, insn)                     \
 do {                                                           \
        __asm__ __volatile__ (                                  \
@@ -164,17 +152,6 @@ do {                                                               \
                : "memory"                                      \
        );                                                      \
 } while (0)
-#else
-#define __put_user_asm(x, addr, err, insn)             \
-do {                                                   \
-       __asm__ __volatile__ (                          \
-               "mov." insn "   %0, %1\n\t"             \
-               : /* no outputs */                      \
-               : "r" (x), "m" (__m(addr))              \
-               : "memory"                              \
-       );                                              \
-} while (0)
-#endif /* CONFIG_MMU */
 
 #if defined(CONFIG_CPU_LITTLE_ENDIAN)
 #define __put_user_u64(val,addr,retval) \