Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag
From: Arnd Bergmann <arnd@arndb.de>
Date: 2020-09-18 14:05:02
Also in:
io-uring, keyrings, linux-arch, linux-arm-kernel, linux-block, linux-fsdevel, linux-mips, linux-mm, linux-s390, linux-scsi, linux-security-module, lkml, netdev, sparclinux
On Fri, Sep 18, 2020 at 3:44 PM Christoph Hellwig [off-list ref] wrote:
On Fri, Sep 18, 2020 at 02:40:12PM +0100, Al Viro wrote:quoted
quoted
/* Vector 0x110 is LINUX_32BIT_SYSCALL_TRAP */ - return pt_regs_trap_type(current_pt_regs()) == 0x110; + return pt_regs_trap_type(current_pt_regs()) == 0x110 || + (current->flags & PF_FORCE_COMPAT);Can't say I like that approach ;-/ Reasoning about the behaviour is much harder when it's controlled like that - witness set_fs() shite...I don't particularly like it either. But do you have a better idea how to deal with io_uring vs compat tasks?
Do we need to worry about something other than the compat_iovec
struct for now? Regarding the code in io_import_iovec(), it would
seem that can easily be handled by exposing an internal helper.
Instead of
#ifdef CONFIG_COMPAT
if (req->ctx->compat)
return compat_import_iovec(rw, buf, sqe_len, UIO_FASTIOV,
iovec, iter);
#endif
return import_iovec(rw, buf, sqe_len, UIO_FASTIOV, iovec, iter);
This could do
__import_iovec(rw, buf, sqe_len, UIO_FASTIOV, iovec,
iter, req->ctx->compat);
With the normal import_iovec() becoming a trivial wrapper around
the same thing:
ssize_t import_iovec(int type, const struct iovec __user * uvector,
unsigned nr_segs, unsigned fast_segs,
struct iovec **iov, struct iov_iter *i)
{
return __import_iovec(type, uvector, nr_segs, fast_segs, iov,
i, in_compat_syscall());
}
Arnd