Hi Paul, thanks for your response! On Mo, 2021-06-28T12:59-0400, Paul Moore wrote: > On Mon, Jun 28, 2021 at 9:25 AM Thomas Weißschuh <linux@xxxxxxxxxxxxxx> wrote: > > > > Hi everyone, > > > > there does not seem to be a way to access the AUDIT_ARCH_ constant that matches > > the currently visible syscall numbers (__NR_...) from the kernel uapi headers. > > Looking at Linus' current tree I see the AUDIT_ARCH_* defines in > include/uapi/linux/audit.h; looking on my system right now I see the > defines in /usr/include/linux/audit.h. What kernel repository and > distribution are you using? I am using ArchLinux and also have all these defines. > > Questions: > > > > Is it really necessary to validate the arch value when syscall numbers are > > already target-specific? > > (If not, should this be added to the docs?) > > Checking the arch/ABI value is important so that you can ensure that > you are using the syscall number in the proper context. For example, > look at the access(2) syscall: it is undefined on some ABIs and can > take either a value of 20, 21, or 33 depending on the arch/ABI. > Unfortunately this is rather common. But when if I am not hardcoding the syscall numbers but use the __NR_access kernel define then I should always get the correct number for the ABI I am compiling for (or an error if the syscall does not exist), no? > Checking the arch/ABI value is also handy if you want to quickly > disallow certain ABIs on a system that supports multiple ABI, e.g. > disabling 32-bit x86 on a 64-bit x86_64 system. > > > Would it make sense to expose the audit arch matching the syscall numbers in > > the uapi headers? > > Yes, which is why the existing headers do so ;) If you don't see the > header files I mentioned above, it may be worth checking your kernel > source repository and your distribution's installed kernel header > files. I do see constants for all the possible ABIs but not one constant that always represents the one I am currently compiling for. The same way the syscall number defines always give me the syscall number for the currently targeted ABI. Thomas
