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

[Guenter Roeck]

On 1/11/24 12:14, Linus Torvalds wrote:
> On Thu, 11 Jan 2024 at 10:57, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > Any variance of put_user() with &buf[ctr] or buf + ctr fails
> > if ctr is a variable and permitted to be != 0.
>
> Crazy. But the 64-bit put_user() is a bit special and tends to require
> more registers (the 64-bit value is passed in two registers), so that
> probably then results in the ICE.
>
> Side note: looking at the SH version of __put_user_u64(), I think it's
> buggy and is missing the exception handler for the second 32-bit move.
> I dunno, I don't read sh asm, but it looks suspicious.

I wonder if something may be wrong with the definition and use of __m
for u64 accesses. The code below also fixes the build problem.

But then I really don't know what

struct __large_struct { unsigned long buf[100]; };
#define __m(x) (*(struct __large_struct __user *)(x))

is supposed to be doing in the first place, and I still don't understand
why the problem only shows up with CONFIG_MMU=n.

Guenter

---
diff --git a/arch/sh/include/asm/uaccess_32.h b/arch/sh/include/asm/uaccess_32.h
index 5d7ddc092afd..f0451a37b6ff 100644
--- a/arch/sh/include/asm/uaccess_32.h
+++ b/arch/sh/include/asm/uaccess_32.h
@@ -196,7 +196,7 @@ __asm__ __volatile__( \
        ".long  1b, 3b\n\t" \
        ".previous" \
        : "=r" (retval) \
-       : "r" (val), "m" (__m(addr)), "i" (-EFAULT), "0" (retval) \
+       : "r" (val), "m" (*(u64 *)(addr)), "i" (-EFAULT), "0" (retval) \
         : "memory"); })
 #else
 #define __put_user_u64(val,addr,retval) \
@@ -218,7 +218,7 @@ __asm__ __volatile__( \
        ".long  1b, 3b\n\t" \
        ".previous" \
        : "=r" (retval) \
-       : "r" (val), "m" (__m(addr)), "i" (-EFAULT), "0" (retval) \
+       : "r" (val), "m" (*(u64 *)(addr)), "i" (-EFAULT), "0" (retval) \
         : "memory"); })
 #endif