Re: [RFC PATCH] sys_read: add a compat_sys_read for 64bit system
From: Zhangjian (Bamvor) <hidden>
Date: 2016-06-08 02:17:55
Also in:
lkml
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
quoted hunk
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 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_closediff --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, 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); +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 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) #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