linux-kernel - [PATCH 4.14 144/164] MIPS: memset.S: Fix clobber of v1 in last

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20180422135141.371839514@linuxfoundation.org>
Date:   Sun, 22 Apr 2018 15:53:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, James Hogan <jhogan@...nel.org>,
        Matt Redfearn <matt.redfearn@...s.com>,
        Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org
Subject: [PATCH 4.14 144/164] MIPS: memset.S: Fix clobber of v1 in last_fixup

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matt Redfearn <matt.redfearn@...s.com>

commit c96eebf07692e53bf4dd5987510d8b550e793598 upstream.

The label .Llast_fixup\@ is jumped to on page fault within the final
byte set loop of memset (on < MIPSR6 architectures). For some reason, in
this fault handler, the v1 register is randomly set to a2 & STORMASK.
This clobbers v1 for the calling function. This can be observed with the
following test code:

static int __init __attribute__((optimize("O0"))) test_clear_user(void)
{
  register int t asm("v1");
  char *test;
  int j, k;

  pr_info("\n\n\nTesting clear_user\n");
  test = vmalloc(PAGE_SIZE);

  for (j = 256; j < 512; j++) {
    t = 0xa5a5a5a5;
    if ((k = clear_user(test + PAGE_SIZE - 256, j)) != j - 256) {
        pr_err("clear_user (%px %d) returned %d\n", test + PAGE_SIZE - 256, j, k);
    }
    if (t != 0xa5a5a5a5) {
       pr_err("v1 was clobbered to 0x%x!\n", t);
    }
  }

  return 0;
}
late_initcall(test_clear_user);

Which demonstrates that v1 is indeed clobbered (MIPS64):

Testing clear_user
v1 was clobbered to 0x1!
v1 was clobbered to 0x2!
v1 was clobbered to 0x3!
v1 was clobbered to 0x4!
v1 was clobbered to 0x5!
v1 was clobbered to 0x6!
v1 was clobbered to 0x7!

Since the number of bytes that could not be set is already contained in
a2, the andi placing a value in v1 is not necessary and actively
harmful in clobbering v1.

Reported-by: James Hogan <jhogan@...nel.org>
Signed-off-by: Matt Redfearn <matt.redfearn@...s.com>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: linux-mips@...ux-mips.org
Cc: stable@...r.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/19109/
Signed-off-by: James Hogan <jhogan@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/mips/lib/memset.S |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/mips/lib/memset.S
+++ b/arch/mips/lib/memset.S
@@ -258,7 +258,7 @@
 
 .Llast_fixup\@:
 	jr		ra
-	andi		v1, a2, STORMASK
+	 nop
 
 .Lsmall_fixup\@:
 	PTR_SUBU	a2, t1, a0