Copy x...@kernel.org > -----Original Message----- > From: David Laight <david.lai...@aculab.com> > Sent: 04 January 2021 12:17 > To: Al Viro <v...@zeniv.linux.org.uk>; Christoph Hellwig <h...@lst.de>; > linux-kernel@vger.kernel.org > Subject: in_compat_syscall() on x86 > > On x86 in_compat_syscall() is defined as: > in_ia32_syscall() || in_x32_syscall() > > Now in_ia32_syscall() is a simple check of the TS_COMPAT flag. > However in_x32_syscall() is a horrid beast that has to indirect > through to the original %eax value (ie the syscall number) and > check for a bit there. > > So on a kernel with x32 support (probably most distro kernels) > the in_compat_syscall() check is rather more expensive than > one might expect. > > It would be muck better if both checks could be done together. > I think this would require the syscall entry code to set a > value in both the 64bit and x32 entry paths. > (Can a process make both 64bit and x32 system calls?) > > To do this sensible (probably) requires a byte be allocated > to hold the syscall type - rather than using flag bits > in the 'status' field. > > Apart from the syscall entry, the exec code seems to change > the syscall type to that of the binary being executed. > I didn't spot anything else that changes the fields. > > But I failed to find the full list of allocated bits for > the 'status' field. > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 > 1PT, UK > Registration No: 1397386 (Wales)
- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
