Re: [RFC PATCH] sys_read: add a compat_sys_read for 64bit system

Hi,

On 2016/6/8 9:33, Weidong Wang wrote:

Test 32 progress and 64 progress on the 64bit system with
this progress:

int main(int argc, char **argv)
{
         int fd = 0;
         int i, ret = 0;
         char buf[512];
         unsigned long count = -1;

         fd = open("/tmp", O_RDONLY);
         if (fd < -1) {
                 printf("Pls check the directory is exist?\n");
                 return -1;
         }
         errno = 0;
         ret = read(fd, NULL, count);
         printf("Ret is %d errno %d\n", ret, errno);
         close(fd);

         return 0;
}

we get the different errno. The 64 progress we get errno is -14 while
the 32 progress is -21.

The reason is that, the user progress would use a 32bit count, while
the sys_read size_t in kernel is 64bit.  When the uesrspace count is
-1(0xffffffff), it goes to the sys_read, it would be change to a positive
number.

So I think we should add a compat_sys_read for the read syscall. I test it
on x86 or arm64 platform. The patch works well.

As weidong said, we tested on x86, x86_64, aarch64 ilp32, aarch64 lp64.
We do not familiar with other architecture, cc linux-api, hope could get more
input.

Regards

Bamvor

On June 7, 2016 7:14:41 PM PDT, "Zhangjian (Bamvor)" [off-list ref] wrote:

Hi,

On 2016/6/8 9:33, Weidong Wang wrote:

quoted

Test 32 progress and 64 progress on the 64bit system with
this progress:

int main(int argc, char **argv)
{
         int fd = 0;
         int i, ret = 0;
         char buf[512];
         unsigned long count = -1;

         fd = open("/tmp", O_RDONLY);
         if (fd < -1) {
                 printf("Pls check the directory is exist?\n");
                 return -1;
         }
         errno = 0;
         ret = read(fd, NULL, count);
         printf("Ret is %d errno %d\n", ret, errno);
         close(fd);

         return 0;
}

we get the different errno. The 64 progress we get errno is -14 while
the 32 progress is -21.

The reason is that, the user progress would use a 32bit count, while
the sys_read size_t in kernel is 64bit.  When the uesrspace count is
-1(0xffffffff), it goes to the sys_read, it would be change to a

positive

quoted

number.

So I think we should add a compat_sys_read for the read syscall. I

test it

quoted

on x86 or arm64 platform. The patch works well.

As weidong said, we tested on x86, x86_64, aarch64 ilp32, aarch64 lp64.
We do not familiar with other architecture, cc linux-api, hope could
get more
input.

Regards

Bamvor

quoted

As well this patch may do work for the 'tile' 64 system.
I think it may enter the same result on mips/parisc/powerpc/sparc.
The s390 do the compat_sys_s390_read for the compat sys_read.

Signed-off-by: Weidong Wang <redacted>
---
  arch/x86/entry/syscalls/syscall_32.tbl | 2 +-
  fs/read_write.c                        | 8 ++++++++
  include/linux/compat.h                 | 2 ++
  include/uapi/asm-generic/unistd.h      | 2 +-
  4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl

b/arch/x86/entry/syscalls/syscall_32.tbl

quoted

index 4cddd17..ebc24e3 100644

--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl

@@ -9,7 +9,7 @@
  0	i386	restart_syscall		sys_restart_syscall
  1	i386	exit			sys_exit
  2	i386	fork			sys_fork			sys_fork
-3	i386	read			sys_read
+3	i386	read			sys_read			compat_sys_read
  4	i386	write			sys_write
  5	i386	open			sys_open			compat_sys_open
  6	i386	close			sys_close

diff --git a/fs/read_write.c b/fs/read_write.c
index 933b53a..d244848 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c

@@ -613,6 +613,14 @@ SYSCALL_DEFINE3(write, unsigned int, fd, const

char __user *, buf,

quoted

  	return ret;
  }

+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf,
+		compat_size_t, count)
+{
+        return sys_read(fd, buf, (compat_ssize_t)count);
+}
+#endif
+
  SYSCALL_DEFINE4(pread64, unsigned int, fd, char __user *, buf,
  			size_t, count, loff_t, pos)
  {

diff --git a/include/linux/compat.h b/include/linux/compat.h
index f964ef7..d88ccad 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h

@@ -332,6 +332,8 @@ asmlinkage long compat_sys_keyctl(u32 option,
  			      u32 arg2, u32 arg3, u32 arg4, u32 arg5);
  asmlinkage long compat_sys_ustat(unsigned dev, struct compat_ustat

__user *u32);

quoted

+asmlinkage ssize_t compat_sys_read(unsigned int fd,
+		char __user * buf, compat_size_t count);
  asmlinkage ssize_t compat_sys_readv(compat_ulong_t fd,
  		const struct compat_iovec __user *vec, compat_ulong_t vlen);
  asmlinkage ssize_t compat_sys_writev(compat_ulong_t fd,

diff --git a/include/uapi/asm-generic/unistd.h

b/include/uapi/asm-generic/unistd.h

quoted

index a26415b..745818a 100644

--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h

@@ -201,7 +201,7 @@ __SC_COMP(__NR_getdents64, sys_getdents64,

compat_sys_getdents64)

quoted

  #define __NR3264_lseek 62
  __SC_3264(__NR3264_lseek, sys_llseek, sys_lseek)
  #define __NR_read 63
-__SYSCALL(__NR_read, sys_read)
+__SC_COMP(__NR_read, sys_read, compat_sys_read)
  #define __NR_write 64
  __SYSCALL(__NR_write, sys_write)
  #define __NR_readv 65

Does this cause any actual problems?  Also, it seems extremely unlikely read() would be the only system call so affected.
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.

Hi, Peter

On 2016/6/8 15:33, H. Peter Anvin wrote:

On June 7, 2016 7:14:41 PM PDT, "Zhangjian (Bamvor)" [off-list ref] wrote:

quoted

Hi,

On 2016/6/8 9:33, Weidong Wang wrote:

quoted

Test 32 progress and 64 progress on the 64bit system with
this progress:

int main(int argc, char **argv)
{
          int fd = 0;
          int i, ret = 0;
          char buf[512];
          unsigned long count = -1;

          fd = open("/tmp", O_RDONLY);
          if (fd < -1) {
                  printf("Pls check the directory is exist?\n");
                  return -1;
          }
          errno = 0;
          ret = read(fd, NULL, count);
          printf("Ret is %d errno %d\n", ret, errno);
          close(fd);

          return 0;
}

we get the different errno. The 64 progress we get errno is -14 while
the 32 progress is -21.

The reason is that, the user progress would use a 32bit count, while
the sys_read size_t in kernel is 64bit.  When the uesrspace count is
-1(0xffffffff), it goes to the sys_read, it would be change to a

positive

quoted

number.

So I think we should add a compat_sys_read for the read syscall. I

test it

quoted

on x86 or arm64 platform. The patch works well.

As weidong said, we tested on x86, x86_64, aarch64 ilp32, aarch64 lp64.
We do not familiar with other architecture, cc linux-api, hope could
get more
input.

Regards

Bamvor

quoted

As well this patch may do work for the 'tile' 64 system.
I think it may enter the same result on mips/parisc/powerpc/sparc.
The s390 do the compat_sys_s390_read for the compat sys_read.

Signed-off-by: Weidong Wang <redacted>
---
   arch/x86/entry/syscalls/syscall_32.tbl | 2 +-
   fs/read_write.c                        | 8 ++++++++
   include/linux/compat.h                 | 2 ++
   include/uapi/asm-generic/unistd.h      | 2 +-
   4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl

b/arch/x86/entry/syscalls/syscall_32.tbl

quoted

index 4cddd17..ebc24e3 100644

--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl

@@ -9,7 +9,7 @@
   0	i386	restart_syscall		sys_restart_syscall
   1	i386	exit			sys_exit
   2	i386	fork			sys_fork			sys_fork
-3	i386	read			sys_read
+3	i386	read			sys_read			compat_sys_read
   4	i386	write			sys_write
   5	i386	open			sys_open			compat_sys_open
   6	i386	close			sys_close

diff --git a/fs/read_write.c b/fs/read_write.c
index 933b53a..d244848 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c

@@ -613,6 +613,14 @@ SYSCALL_DEFINE3(write, unsigned int, fd, const

char __user *, buf,

quoted

   	return ret;
   }

+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf,
+		compat_size_t, count)
+{
+        return sys_read(fd, buf, (compat_ssize_t)count);
+}
+#endif
+
   SYSCALL_DEFINE4(pread64, unsigned int, fd, char __user *, buf,
   			size_t, count, loff_t, pos)
   {

diff --git a/include/linux/compat.h b/include/linux/compat.h
index f964ef7..d88ccad 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h

@@ -332,6 +332,8 @@ asmlinkage long compat_sys_keyctl(u32 option,
   			      u32 arg2, u32 arg3, u32 arg4, u32 arg5);
   asmlinkage long compat_sys_ustat(unsigned dev, struct compat_ustat

__user *u32);

quoted

+asmlinkage ssize_t compat_sys_read(unsigned int fd,
+		char __user * buf, compat_size_t count);
   asmlinkage ssize_t compat_sys_readv(compat_ulong_t fd,
   		const struct compat_iovec __user *vec, compat_ulong_t vlen);
   asmlinkage ssize_t compat_sys_writev(compat_ulong_t fd,

diff --git a/include/uapi/asm-generic/unistd.h

b/include/uapi/asm-generic/unistd.h

quoted

index a26415b..745818a 100644

--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h

@@ -201,7 +201,7 @@ __SC_COMP(__NR_getdents64, sys_getdents64,

compat_sys_getdents64)

quoted

   #define __NR3264_lseek 62
   __SC_3264(__NR3264_lseek, sys_llseek, sys_lseek)
   #define __NR_read 63
-__SYSCALL(__NR_read, sys_read)
+__SC_COMP(__NR_read, sys_read, compat_sys_read)
   #define __NR_write 64
   __SYSCALL(__NR_write, sys_write)
   #define __NR_readv 65

Does this cause any actual problems?  Also, it seems extremely unlikely read() would be the only system call so affected.

It do not cause any actual problems. And write may be affected too.
Without this patch, the errno is different when 32 application migrate
from 32bit kernel to 64bit kernel.

Regards

Bamvor

On Tue, Jun 7, 2016 at 7:14 PM, Zhangjian (Bamvor)
[off-list ref] wrote:

Hi,

On 2016/6/8 9:33, Weidong Wang wrote:

quoted

Test 32 progress and 64 progress on the 64bit system with
this progress:

int main(int argc, char **argv)
{
         int fd = 0;
         int i, ret = 0;
         char buf[512];
         unsigned long count = -1;

         fd = open("/tmp", O_RDONLY);
         if (fd < -1) {
                 printf("Pls check the directory is exist?\n");
                 return -1;
         }
         errno = 0;
         ret = read(fd, NULL, count);
         printf("Ret is %d errno %d\n", ret, errno);
         close(fd);

         return 0;
}

we get the different errno. The 64 progress we get errno is -14 while
the 32 progress is -21.

On 64-bit, you get -14 == -EFAULT.  Seems reasonable: you passed a bad pointer.

On 32-bit, you get -21 == -EISDIR.  Also seems reasonable: fd is a directory.

quoted

The reason is that, the user progress would use a 32bit count, while
the sys_read size_t in kernel is 64bit.  When the uesrspace count is
-1(0xffffffff), it goes to the sys_read, it would be change to a positive
number.

That parameter is size_t, which is unsigned.  It's a positive number
in both cases.

I don't think there's a bug here.

On 2016/6/10 1:08, Andy Lutomirski wrote:

On Tue, Jun 7, 2016 at 7:14 PM, Zhangjian (Bamvor)
[off-list ref] wrote:

quoted

Hi,

On 2016/6/8 9:33, Weidong Wang wrote:

quoted

Test 32 progress and 64 progress on the 64bit system with
this progress:

int main(int argc, char **argv)
{
         int fd = 0;
         int i, ret = 0;
         char buf[512];
         unsigned long count = -1;

         fd = open("/tmp", O_RDONLY);
         if (fd < -1) {
                 printf("Pls check the directory is exist?\n");
                 return -1;
         }
         errno = 0;
         ret = read(fd, NULL, count);
         printf("Ret is %d errno %d\n", ret, errno);
         close(fd);

         return 0;
}

we get the different errno. The 64 progress we get errno is -14 while
the 32 progress is -21.

On 64-bit, you get -14 == -EFAULT.  Seems reasonable: you passed a bad pointer.

On 32-bit, you get -21 == -EISDIR.  Also seems reasonable: fd is a directory.

quoted

quoted

The reason is that, the user progress would use a 32bit count, while
the sys_read size_t in kernel is 64bit.  When the uesrspace count is
-1(0xffffffff), it goes to the sys_read, it would be change to a positive
number.

That parameter is size_t, which is unsigned.  It's a positive number
in both cases.

I don't think there's a bug here.

Yep.
In the progress open the '/tmp' is a directory. If we do open a file '/tmp/files' (exist file),
the result would be different on x86-64bit machine.

On 64-bit, we get -14 == -EFAULT.
On 32-bit, we get the length of the file, the errno is 0.

Regards,
Weidong

.