[v6,13/25] powerpc: Remove direct call to mmap2 syscall handlers

Syscall handlers should not be invoked internally by their symbol names,
as these symbols defined by the architecture-defined SYSCALL_DEFINE
macro. Move the compatibility syscall definition for mmap2 to
syscalls.c, so that all mmap implementations can share a helper function.

Remove 'inline' on static mmap helper.

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
---
V2: Move mmap2 compat implementation to asm/kernel/syscalls.c.
V4: Move to be applied before syscall wrapper introduced.
V5: Remove 'inline' in helper.
---
 arch/powerpc/kernel/sys_ppc32.c |  9 ---------
 arch/powerpc/kernel/syscalls.c  | 17 ++++++++++++++---
 2 files changed, 14 insertions(+), 12 deletions(-)

Rohan McLure <rmclure@linux.ibm.com> writes:
> Syscall handlers should not be invoked internally by their symbol names,
> as these symbols defined by the architecture-defined SYSCALL_DEFINE
> macro. Move the compatibility syscall definition for mmap2 to
> syscalls.c, so that all mmap implementations can share a helper function.
>
> Remove 'inline' on static mmap helper.
>
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
> ---
> V2: Move mmap2 compat implementation to asm/kernel/syscalls.c.
> V4: Move to be applied before syscall wrapper introduced.
> V5: Remove 'inline' in helper.
> ---
>  arch/powerpc/kernel/sys_ppc32.c |  9 ---------
>  arch/powerpc/kernel/syscalls.c  | 17 ++++++++++++++---
>  2 files changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/arch/powerpc/kernel/sys_ppc32.c b/arch/powerpc/kernel/sys_ppc32.c
> index d961634976d8..776ae7565fc5 100644
> --- a/arch/powerpc/kernel/sys_ppc32.c
> +++ b/arch/powerpc/kernel/sys_ppc32.c
> @@ -25,7 +25,6 @@
>  #include <linux/poll.h>
>  #include <linux/personality.h>
>  #include <linux/stat.h>
> -#include <linux/mman.h>
>  #include <linux/in.h>
>  #include <linux/syscalls.h>
>  #include <linux/unistd.h>
> @@ -48,14 +47,6 @@
>  #include <asm/syscalls.h>
>  #include <asm/switch_to.h>
>  
> -unsigned long compat_sys_mmap2(unsigned long addr, size_t len,
> -			  unsigned long prot, unsigned long flags,
> -			  unsigned long fd, unsigned long pgoff)
> -{
> -	/* This should remain 12 even if PAGE_SIZE changes */
> -	return sys_mmap(addr, len, prot, flags, fd, pgoff << 12);
> -}
> -
>  compat_ssize_t compat_sys_pread64(unsigned int fd, char __user *ubuf, compat_size_t count,
>  			     u32 reg6, u32 pos1, u32 pos2)
>  {
> diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c
> index a04c97faa21a..9830957498b0 100644
> --- a/arch/powerpc/kernel/syscalls.c
> +++ b/arch/powerpc/kernel/syscalls.c
> @@ -36,9 +36,9 @@
>  #include <asm/time.h>
>  #include <asm/unistd.h>
>  
> -static inline long do_mmap2(unsigned long addr, size_t len,
> -			unsigned long prot, unsigned long flags,
> -			unsigned long fd, unsigned long off, int shift)
> +static long do_mmap2(unsigned long addr, size_t len,
> +		     unsigned long prot, unsigned long flags,
> +		     unsigned long fd, unsigned long off, int shift)
>  {
>  	if (!arch_validate_prot(prot, addr))
>  		return -EINVAL;
> @@ -56,6 +56,17 @@ SYSCALL_DEFINE6(mmap2, unsigned long, addr, size_t, len,
>  	return do_mmap2(addr, len, prot, flags, fd, pgoff, PAGE_SHIFT-12);
>  }
>  
> +#ifdef CONFIG_COMPAT
> +COMPAT_SYSCALL_DEFINE6(mmap2,
> +		       unsigned long, addr, size_t, len,
> +		       unsigned long, prot, unsigned long, flags,
> +		       unsigned long, fd, unsigned long, pgoff)
> +{
> +	/* This should remain 12 even if PAGE_SIZE changes */
> +	return do_mmap2(addr, len, prot, flags, fd, pgoff << 12, PAGE_SHIFT-12);

This isn't quite right.

The comment about it remaining 12 is kind of misleading, it was true
when compat_sys_mmap2() called sys_mmap(), but it's wrong now that we're
calling do_mmap2().

The incoming "pgoff" here is in units of 4K.

do_mmap2() takes "off" in whatever units, but also takes "shift", which
has to tell us how to shift "off" into PAGE_SIZE units.

If we pass off = pgoff << 12, that's in bytes, so we need to page
shift = PAGE_SHIFT.

But I think it makes more sense to do the same as mmap2() and pass the
4K offset through, and pass shift = PAGE_SHIFT - 12. I also borrowed the
"off_4k" name from arm64. End result:

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE6(mmap2,
		       unsigned long, addr, size_t, len,
		       unsigned long, prot, unsigned long, flags,
		       unsigned long, fd, unsigned long, off_4k)
{
	return do_mmap2(addr, len, prot, flags, fd, off_4k, PAGE_SHIFT-12);
}
#endif

With that my G5 boots again :)

cheers

On Wed, Sep 28, 2022, at 2:15 PM, Michael Ellerman wrote:

> But I think it makes more sense to do the same as mmap2() and pass the
> 4K offset through, and pass shift = PAGE_SHIFT - 12. I also borrowed the
> "off_4k" name from arm64. End result:
>
> #ifdef CONFIG_COMPAT
> COMPAT_SYSCALL_DEFINE6(mmap2,
> 		       unsigned long, addr, size_t, len,
> 		       unsigned long, prot, unsigned long, flags,
> 		       unsigned long, fd, unsigned long, off_4k)
> {
> 	return do_mmap2(addr, len, prot, flags, fd, off_4k, PAGE_SHIFT-12);
> }
> #endif
>
> With that my G5 boots again :)

Any chance we can instead add a working compat_sys_mmap2/sys_mmap2
in mm/mmap.c alongside the sys_mmap_pgoff implementation?

While sys_mmap_pgoff() was meant to replace the various sys_mmap2()
implementations, I think it was ultimately a mistake, and we later
converged on the sys_mmap2() calling conventions with 12 bits
offset for almost all 32-bit architectures.

   Arnd

"Arnd Bergmann" <arnd@arndb.de> writes:
> On Wed, Sep 28, 2022, at 2:15 PM, Michael Ellerman wrote:
>
>> But I think it makes more sense to do the same as mmap2() and pass the
>> 4K offset through, and pass shift = PAGE_SHIFT - 12. I also borrowed the
>> "off_4k" name from arm64. End result:
>>
>> #ifdef CONFIG_COMPAT
>> COMPAT_SYSCALL_DEFINE6(mmap2,
>> 		       unsigned long, addr, size_t, len,
>> 		       unsigned long, prot, unsigned long, flags,
>> 		       unsigned long, fd, unsigned long, off_4k)
>> {
>> 	return do_mmap2(addr, len, prot, flags, fd, off_4k, PAGE_SHIFT-12);
>> }
>> #endif
>>
>> With that my G5 boots again :)
>
> Any chance we can instead add a working compat_sys_mmap2/sys_mmap2
> in mm/mmap.c alongside the sys_mmap_pgoff implementation?

I've merged this, but happy to clean things up in a subsequent patch :)

> While sys_mmap_pgoff() was meant to replace the various sys_mmap2()
> implementations, I think it was ultimately a mistake, and we later
> converged on the sys_mmap2() calling conventions with 12 bits
> offset for almost all 32-bit architectures.

I only see 3 compat mmap2s:

  $ gg "COMPAT_SYSCALL.*mmap2"
  arch/arm64/kernel/sys32.c:COMPAT_SYSCALL_DEFINE6(aarch32_mmap2, unsigned long, addr, unsigned long, len,
  arch/powerpc/kernel/syscalls.c:COMPAT_SYSCALL_DEFINE6(mmap2, unsigned long, addr, size_t, len,
  arch/s390/kernel/compat_linux.c:COMPAT_SYSCALL_DEFINE1(s390_mmap2, struct mmap_arg_struct_emu31 __user *, arg)

s390 is weird.

The arm64 one and ours are similar, but we have the additional call to
arch_validate_prot(prot, addr). arm64 does implement arch_validate_prot().

Similar with mmap2, we call arch_validate_prot() but no one else does (why not?).

cheers

On Fri, Sep 30, 2022, at 3:19 PM, Michael Ellerman wrote:
> "Arnd Bergmann" <arnd@arndb.de> writes:
>>
>> While sys_mmap_pgoff() was meant to replace the various sys_mmap2()
>> implementations, I think it was ultimately a mistake, and we later
>> converged on the sys_mmap2() calling conventions with 12 bits
>> offset for almost all 32-bit architectures.
>
> I only see 3 compat mmap2s:
>
>   $ gg "COMPAT_SYSCALL.*mmap2"
>   arch/arm64/kernel/sys32.c:COMPAT_SYSCALL_DEFINE6(aarch32_mmap2, 
> unsigned long, addr, unsigned long, len,
>   arch/powerpc/kernel/syscalls.c:COMPAT_SYSCALL_DEFINE6(mmap2, unsigned 
> long, addr, size_t, len,
>   arch/s390/kernel/compat_linux.c:COMPAT_SYSCALL_DEFINE1(s390_mmap2, 
> struct mmap_arg_struct_emu31 __user *, arg)

They are all inconsistently named, and some are shared with the 64-bit
implementation on architectures that provide mmap2 for both 32-bit
and 64-bit mode, rather than only for 32-bit.

arch/mips/kernel/syscall.c:SYSCALL_DEFINE6(mips_mmap2, unsigned long, addr, unsigned long, len,
arch/sparc/kernel/sys32.S:      .globl          sys32_mmap2
arch/parisc/kernel/sys_parisc.c:asmlinkage unsigned long sys_mmap2(unsigned long addr, unsigned long len,

> s390 is weird.

Right, they used to be limited to 5 register arguments

> The arm64 one and ours are similar, but we have the additional call to
> arch_validate_prot(prot, addr). arm64 does implement arch_validate_prot().
>
> Similar with mmap2, we call arch_validate_prot() but no one else does 
> (why not?).

This looks like it was added in ef3d3246a0d0 ("powerpc/mm: Add Strong
Access Ordering support"), which is powerpc specific. It looks like
this should correspond to a custom arch_calc_vm_prot_bits()
implementation, which exists on arm64, powerpc, sparc and x86.

I suppose it should be there for those four.

    Arnd