rseq: Use __u64 for rseq_cs fields, validate user inputs

Change the rseq ABI so rseq_cs start_ip, post_commit_offset and abort_ip
fields are seen as 64-bit fields by both 32-bit and 64-bit kernels rather
that ignoring the 32 upper bits on 32-bit kernels. This ensures we have a
consistent behavior for a 32-bit binary executed on 32-bit kernels and in
compat mode on 64-bit kernels.

Validating the value of abort_ip field to be below TASK_SIZE ensures the
kernel don't return to an invalid address when returning to userspace
after an abort. I don't fully trust each architecture code to consistently
deal with invalid return addresses.

Validating the value of the start_ip and post_commit_offset fields
prevents overflow on arithmetic performed on those values, used to
check whether abort_ip is within the rseq critical section.

If validation fails, the process is killed with a segmentation fault.

When the signature encountered before abort_ip does not match the expected
signature, return -EINVAL rather than -EPERM to be consistent with other
input validation return codes from rseq_get_rseq_cs().

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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