On Fri, Oct 13, 2017 at 5:03 PM, Andy Lutomirski <[email protected]> wrote: > On Fri, Oct 13, 2017 at 1:39 PM, Dave Hansen > <[email protected]> wrote: >> >> I noticed that we don't have tracepoints for sys_modify_ldt(). I >> think that's because we define it directly instead of using the >> normal SYSCALL_DEFINEx() macros. >> >> Is there a reason for that, or were they just missed when the >> macros were created? > > No, and it's a longstanding fsckup that I think you can't fix like > this because... > >> >> Cc: [email protected] >> Cc: Andy Lutomirski <[email protected]> >> >> --- >> >> b/arch/x86/include/asm/syscalls.h | 2 +- >> b/arch/x86/kernel/ldt.c | 5 +++-- >> b/arch/x86/um/ldt.c | 3 ++- >> 3 files changed, 6 insertions(+), 4 deletions(-) >> >> diff -puN arch/x86/kernel/ldt.c~x86-syscall-macros-modify_ldt >> arch/x86/kernel/ldt.c >> --- a/arch/x86/kernel/ldt.c~x86-syscall-macros-modify_ldt 2017-10-13 >> 13:30:12.802553391 -0700 >> +++ b/arch/x86/kernel/ldt.c 2017-10-13 13:30:12.817553391 -0700 >> @@ -12,6 +12,7 @@ >> #include <linux/string.h> >> #include <linux/mm.h> >> #include <linux/smp.h> >> +#include <linux/syscalls.h> >> #include <linux/slab.h> >> #include <linux/vmalloc.h> >> #include <linux/uaccess.h> >> @@ -294,8 +295,8 @@ out: >> return error; >> } >> >> -asmlinkage int sys_modify_ldt(int func, void __user *ptr, >> - unsigned long bytecount) >> +SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr , >> + unsigned long , bytecount) > > sys_modify_ldt() returns int, which is wrong, and it's visibly wrong > to 64-bit user code. So I think you need to make sure that the return > value is cast to int in all cases.
I don't think there will be a problem here. If 64-bit userspace treats it as an int, it will truncate to 32-bit signed and all is well. If it is treating it as a long, then it's currently broken for errors anyways. -- Brian Gerst
