Patch "MIPS: Guard against any partial write attempt with PTRACE_SETREGSET" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    MIPS: Guard against any partial write attempt with PTRACE_SETREGSET

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mips-guard-against-any-partial-write-attempt-with-ptrace_setregset.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From dc24d0edf33c3e15099688b6bbdf7bdc24bf6e91 Mon Sep 17 00:00:00 2001
From: "Maciej W. Rozycki" <macro@mips.com>
Date: Mon, 11 Dec 2017 22:52:15 +0000
Subject: MIPS: Guard against any partial write attempt with PTRACE_SETREGSET

From: Maciej W. Rozycki <macro@mips.com>

commit dc24d0edf33c3e15099688b6bbdf7bdc24bf6e91 upstream.

Complement commit d614fd58a283 ("mips/ptrace: Preserve previous
registers for short regset write") and ensure that no partial register
write attempt is made with PTRACE_SETREGSET, as we do not preinitialize
any temporaries used to hold incoming register data and consequently
random data could be written.

It is the responsibility of the caller, such as `ptrace_regset', to
arrange for writes to span whole registers only, so here we only assert
that it has indeed happened.

Signed-off-by: Maciej W. Rozycki <macro@mips.com>
Fixes: 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset")
Cc: James Hogan <james.hogan@mips.com>
Cc: Paul Burton <Paul.Burton@mips.com>
Cc: Alex Smith <alex@alex-smith.me.uk>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17926/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/kernel/ptrace.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -536,7 +536,15 @@ static int fpr_set_msa(struct task_struc
 	return 0;
 }
 
-/* Copy the supplied NT_PRFPREG buffer to the floating-point context.  */
+/*
+ * Copy the supplied NT_PRFPREG buffer to the floating-point context.
+ *
+ * We optimize for the case where `count % sizeof(elf_fpreg_t) == 0',
+ * which is supposed to have been guaranteed by the kernel before
+ * calling us, e.g. in `ptrace_regset'.  We enforce that requirement,
+ * so that we can safely avoid preinitializing temporaries for
+ * partial register writes.
+ */
 static int fpr_set(struct task_struct *target,
 		   const struct user_regset *regset,
 		   unsigned int pos, unsigned int count,
@@ -544,6 +552,8 @@ static int fpr_set(struct task_struct *t
 {
 	int err;
 
+	BUG_ON(count % sizeof(elf_fpreg_t));
+
 	/* XXX fcr31  */
 
 	init_fp_ctx(target);


Patches currently in stable-queue which might be from macro@mips.com are

queue-4.9/mips-consistently-handle-buffer-counter-with-ptrace_setregset.patch
queue-4.9/mips-disallow-outsized-ptrace_setregset-nt_prfpreg-regset-accesses.patch
queue-4.9/mips-guard-against-any-partial-write-attempt-with-ptrace_setregset.patch
queue-4.9/mips-also-verify-sizeof-elf_fpreg_t-with-ptrace_setregset.patch
queue-4.9/mips-factor-out-nt_prfpreg-regset-access-helpers.patch
queue-4.9/mips-validate-pr_set_fp_mode-prctl-2-requests-against-the-abi-of-the-task.patch
queue-4.9/mips-fix-an-fcsr-access-api-regression-with-nt_prfpreg-and-msa.patch