Messages in this thread | | | Date | Mon, 24 Jan 2022 07:19:15 +0100 | From | Greg KH <> | Subject | Re: [RFC PATCH] rseq: Fix broken uapi field layout on 32-bit little endian |
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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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