rseq: uapi: Declare rseq_cs field as union, update includes

Declaring the rseq_cs field as a union between __u64 and two __u32
allows both 32-bit and 64-bit kernels to read the full __u64, and
therefore validate that a 32-bit user-space cleared the upper 32
bits, thus ensuring a consistent behavior between native 32-bit
kernels and 32-bit compat tasks on 64-bit kernels.

Check that the rseq_cs value read is < TASK_SIZE.

The asm/byteorder.h header needs to be included by rseq.h, now
that it is not using linux/types_32_64.h anymore.

Considering that only __32 and __u64 types are declared in linux/rseq.h,
the linux/types.h header should always be included for both kernel and
user-space code: including stdint.h is just for u64 and u32, which are
not used in this header at all.

Use copy_from_user()/clear_user() to interact with a 64-bit field,
because arm32 does not implement 64-bit __get_user, and ppc32 does not
64-bit get_user. Considering that the rseq_cs pointer does not need to
be loaded/stored with single-copy atomicity from the kernel anymore, we
can simply use copy_from_user()/clear_user().

Signed-off-by: Mathieu Desnoyers <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: Peter Zijlstra <[email protected]>
Cc: "Paul E . McKenney" <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Watson <[email protected]>
Cc: Paul Turner <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Russell King <[email protected]>
Cc: "H . Peter Anvin" <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Chris Lameter <[email protected]>
Cc: Ben Maurer <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Josh Triplett <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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