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[PATCH 3.14 01/23] MIPS: math-emu: Fix jalr emulation when rd == $0

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

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

From: Paul Burton <paul.burton@imgtec.com>

commit ab4a92e66741b35ca12f8497896bafbe579c28a1 upstream.

When emulating a jalr instruction with rd == $0, the code in
isBranchInstr was incorrectly writing to GPR $0 which should actually
always remain zeroed. This would lead to any further instructions
emulated which use $0 operating on a bogus value until the task is next
context switched, at which point the value of $0 in the task context
would be restored to the correct zero by a store in SAVE_SOME. Fix this
by not writing to rd if it is $0.

Fixes: 102cedc32a6e ("MIPS: microMIPS: Floating point support.")
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Maciej W. Rozycki <macro@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13160/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/math-emu/cp1emu.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -676,9 +676,11 @@ static int isBranchInstr(struct pt_regs
 	case spec_op:
 		switch (insn.r_format.func) {
 		case jalr_op:
-			regs->regs[insn.r_format.rd] =
-				regs->cp0_epc + dec_insn.pc_inc +
-				dec_insn.next_pc_inc;
+			if (insn.r_format.rd != 0) {
+				regs->regs[insn.r_format.rd] =
+					regs->cp0_epc + dec_insn.pc_inc +
+					dec_insn.next_pc_inc;
+			}
 			/* Fall through */
 		case jr_op:
 			*contpc = regs->regs[insn.r_format.rs];

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[PATCH 3.14 00/23] 3.14.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-05 23:50 +0200
  [PATCH 3.14 07/23] aacraid: Fix for aac_command_thread hang Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-05 23:50 +0200
  [PATCH 3.14 11/23] pipe: Fix buffer offset after partially failed read Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-05 23:50 +0200
    Re: [PATCH 3.14 11/23] pipe: Fix buffer offset after partially failed  read Jiri Slaby <jslaby@suse.cz> - 2016-06-07 16:00 +0200
      Re: [PATCH 3.14 11/23] pipe: Fix buffer offset after partially  failed read Ben Hutchings <ben@decadent.org.uk> - 2016-06-07 16:50 +0200
  [PATCH 3.14 08/23] cpuidle: Indicate when a device has been unregistered Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-05 23:50 +0200
  [PATCH 3.14 03/23] MIPS: ath79: make bootconsole wait for both THRE and TEMT Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 05/23] ath5k: Change led pin configuration for compaq c700 laptop Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 19/23] ext4: silence UBSAN in ext4_mb_init() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 04/23] Input: uinput - handle compat ioctl for UI_SET_PHYS Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 13/23] xen/events: Dont move disabled irqs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 10/23] rtlwifi: Fix logic error in enter/exit power-save mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 01/23] MIPS: math-emu: Fix jalr emulation when rd == $0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 06/23] aacraid: Relinquish CPU during timeout wait Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 17/23] ext4: fix hang when processing corrupted orphaned inode list Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 02/23] MIPS: Fix siginfo.h to use strict posix types Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 18/23] ext4: address UBSAN warning in mb_find_order_for_block() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 15/23] drm/gma500: Fix possible out of bounds read Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  Re: [PATCH 3.14 00/23] 3.14.72-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2016-06-06 19:30 +0200
    Re: [PATCH 3.14 00/23] 3.14.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-08 02:30 +0200
  Re: [PATCH 3.14 00/23] 3.14.72-stable review Guenter Roeck <linux@roeck-us.net> - 2016-06-07 05:50 +0200

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