On Sun, Jan 23, 2022 at 02:31:54PM -0500, Mathieu Desnoyers wrote:
The rseq rseq_cs.ptr.{ptr32,padding} uapi endianness handling is entirely wrong on 32-bit little endian: a preprocessor logic mistake wrongly uses the big endian field layout on 32-bit little endian architectures.
Fortunately, those ptr32 accessors were never used within the kernel, and only meant as a convenience for user-space.
While working on fixing the ppc32 support in librseq [1], I made sure all 32-bit little endian architectures stopped depending on little endian byte ordering by using the ptr32 field. It led me to discover this wrong ptr32 field ordering on little endian.
Because it is already exposed as a UAPI, all we can do for the existing fields is document the wrong behavior and encourage users to use alternative mechanisms.
Introduce a new rseq_cs.arch field with correct field ordering. Use this opportunity to improve the layout so accesses to architecture fields on both 32-bit and 64-bit architectures are done through the same field hierarchy, which is much nicer than the previous scheme.
The intended use is now:
rseq_thread_area->rseq_cs.ptr64: Access the 64-bit value of the rseq_cs pointer. Available on all architectures (unchanged).
rseq_thread_area->rseq_cs.arch.ptr: Access the architecture specific layout of the rseq_cs pointer. This is a 32-bit field on 32-bit architectures, and a 64-bit field on 64-bit architectures.
Link: https://git.kernel.org/pub/scm/libs/librseq/librseq.git/ [1] Fixes: ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union, update includes") Signed-off-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Florian Weimer fw@deneb.enyo.de Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-api@vger.kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Boqun Feng boqun.feng@gmail.com Cc: Andy Lutomirski luto@amacapital.net Cc: Dave Watson davejwatson@fb.com Cc: Paul Turner pjt@google.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Russell King linux@arm.linux.org.uk Cc: "H . Peter Anvin" hpa@zytor.com Cc: Andi Kleen andi@firstfloor.org Cc: Christian Brauner christian.brauner@ubuntu.com Cc: Ben Maurer bmaurer@fb.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Josh Triplett josh@joshtriplett.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will.deacon@arm.com Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Joel Fernandes joelaf@google.com Cc: Paul E. McKenney paulmck@kernel.org
include/uapi/linux/rseq.h | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)
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This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly.
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