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Re: [PATCH] posix: Fix large mmap64 offset for mips64n32 (BZ#24699)


Ping, I have added it as a release blocker for 2.30.

On 19/06/2019 11:13, Adhemerval Zanella wrote:
> The fix for BZ#21270 (commit 158d5fa0e19) added a mask to avoid offset larger
> than 1^44 to be used along __NR_mmap2.  However mips64n32 users __NR_mmap,
> as mips64n64, but still defines off_t as old non-LFS type (other ILP32, such
> x32, defines off_t being equal to off64_t).  This leads to use the same
> mask meant only for __NR_mmap2 call for __NR_mmap, thus limiting the maximum
> offset it can use with mmap64.
> 
> This patch fixes by setting the high mask only for __NR_mmap2 usage. The
> posix/tst-mmap-offset.c already tests it and also fails for mips64n32. The
> patch also change the test to check for an arch-specific header that defines
> the maximum supported offset.
> 
> Checked on x86_64-linux-gnu, i686-linux-gnu, and I also tests tst-mmap-offset
> on qemu simulated mips64 with kernel 3.2.0 kernel for both mips-linux-gnu and
> mips64-n32-linux-gnu.
> 
> 	[BZ #24699]
> 	* posix/tst-mmap-offset.c: Mention BZ #24699.
> 	(do_test_bz21270): Rename to do_test_large_offset and use
> 	mmap64_maximum_offset to check for maximum expected offset value.
> 	* sysdeps/generic/mmap_info.h: New file.
> 	* sysdeps/unix/sysv/linux/mips/mmap_info.h: Likewise.
> 	* sysdeps/unix/sysv/linux/mmap64.c (MMAP_OFF_HIGH_MASK): Define iff
> 	__NR_mmap2 is used.
> ---
>  posix/tst-mmap-offset.c                  |  9 +++++----
>  sysdeps/generic/mmap_info.h              | 16 ++++++++++++++++
>  sysdeps/unix/sysv/linux/mips/mmap_info.h | 13 +++++++++++++
>  sysdeps/unix/sysv/linux/mmap64.c         |  9 ++++++++-
>  4 files changed, 42 insertions(+), 5 deletions(-)
>  create mode 100644 sysdeps/generic/mmap_info.h
>  create mode 100644 sysdeps/unix/sysv/linux/mips/mmap_info.h
> 
> diff --git a/posix/tst-mmap-offset.c b/posix/tst-mmap-offset.c
> index 676c52845f..d4e53c3e67 100644
> --- a/posix/tst-mmap-offset.c
> +++ b/posix/tst-mmap-offset.c
> @@ -1,4 +1,4 @@
> -/* BZ #18877 and #21270 mmap offset test.
> +/* BZ #18877, BZ #21270, and BZ #24699 mmap offset test.
>  
>     Copyright (C) 2015-2019 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
> @@ -24,6 +24,7 @@
>  #include <unistd.h>
>  #include <errno.h>
>  #include <sys/mman.h>
> +#include <mmap_info.h>
>  
>  #include <support/check.h>
>  
> @@ -76,7 +77,7 @@ do_test_bz18877 (void)
>  
>  /* Check if invalid offset are handled correctly by mmap.  */
>  static int
> -do_test_bz21270 (void)
> +do_test_large_offset (void)
>  {
>    /* For architectures with sizeof (off_t) < sizeof (off64_t) mmap is
>       implemented with __SYS_mmap2 syscall and the offset is represented in
> @@ -90,7 +91,7 @@ do_test_bz21270 (void)
>    const size_t length = 4096;
>  
>    void *addr = mmap64 (NULL, length, prot, flags, fd, offset);
> -  if (sizeof (off_t) < sizeof (off64_t))
> +  if (mmap64_maximum_offset (page_shift) < UINT64_MAX)
>      {
>        if ((addr != MAP_FAILED) && (errno != EINVAL))
>  	FAIL_RET ("mmap succeed");
> @@ -110,7 +111,7 @@ do_test (void)
>    int ret = 0;
>  
>    ret += do_test_bz18877 ();
> -  ret += do_test_bz21270 ();
> +  ret += do_test_large_offset ();
>  
>    return ret;
>  }
> diff --git a/sysdeps/generic/mmap_info.h b/sysdeps/generic/mmap_info.h
> new file mode 100644
> index 0000000000..9a3315a8fe
> --- /dev/null
> +++ b/sysdeps/generic/mmap_info.h
> @@ -0,0 +1,16 @@
> +/* As default architectures with sizeof (off_t) < sizeof (off64_t) the mmap is
> +   implemented with __SYS_mmap2 syscall and the offset is represented in
> +   multiples of page size.  For offset larger than
> +   '1 << (page_shift + 8 * sizeof (off_t))' (that is, 1<<44 on system with
> +   page size of 4096 bytes) the system call silently truncates the offset.
> +   For this case, glibc mmap implementation returns EINVAL.  */
> +
> +/* Return the maximum value expected as offset argument in mmap64 call.  */
> +uint64_t static inline
> +mmap64_maximum_offset (long int page_shift)
> +{
> +  if (sizeof (off_t) < sizeof (off64_t))
> +    return (UINT64_C(1) << (page_shift + (8 * sizeof (off_t)))) - 1;
> +  else
> +    return UINT64_MAX;
> +}
> diff --git a/sysdeps/unix/sysv/linux/mips/mmap_info.h b/sysdeps/unix/sysv/linux/mips/mmap_info.h
> new file mode 100644
> index 0000000000..6fd3c3d954
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/mips/mmap_info.h
> @@ -0,0 +1,13 @@
> +/* mips64n32 uses __NR_mmap for mmap64 while still having sizeof (off_t)
> +   smaller than sizeof (off64_t).  So it allows mapping large offsets
> +   using mmap64 than 32-bit archs which uses __NR_mmap2.  */
> +
> +uint64_t static inline
> +mmap64_maximum_offset (long int page_shift)
> +{
> +#if _MIPS_SIM == _ABIN32 || _MIPS_SIM == _ABI64
> +  return UINT64_MAX;
> +#else
> +  return (UINT64_C(1) << (page_shift + (8 * sizeof (off_t)))) - 1;
> +#endif
> +}
> diff --git a/sysdeps/unix/sysv/linux/mmap64.c b/sysdeps/unix/sysv/linux/mmap64.c
> index cb56540119..671db2b654 100644
> --- a/sysdeps/unix/sysv/linux/mmap64.c
> +++ b/sysdeps/unix/sysv/linux/mmap64.c
> @@ -23,11 +23,18 @@
>  #include <sysdep.h>
>  #include <mmap_internal.h>
>  
> +#ifdef __NR_mmap2
>  /* To avoid silent truncation of offset when using mmap2, do not accept
>     offset larger than 1 << (page_shift + off_t bits).  For archictures with
>     32 bits off_t and page size of 4096 it would be 1^44.  */
> -#define MMAP_OFF_HIGH_MASK \
> +# define MMAP_OFF_HIGH_MASK \
>    ((-(MMAP2_PAGE_UNIT << 1) << (8 * sizeof (off_t) - 1)))
> +#else
> +/* Some ABIs might use __NR_mmap while having sizeof (off_t) smaller than
> +   sizeof (off64_t) (currently only MIPS64n32).  For this case just set
> +   zero the higher bits so mmap with large offset does not fail.  */
> +# define MMAP_OFF_HIGH_MASK  0x0
> +#endif
>  
>  #define MMAP_OFF_MASK (MMAP_OFF_HIGH_MASK | MMAP_OFF_LOW_MASK)
>  
> 


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