linux-kernel - [PATCH 2/3] MIPS: Correct the 64-bit DSP accumulator register size

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Message-ID: <alpine.DEB.2.00.1805102026260.10896@tp.orcam.me.uk>
Date:   Tue, 15 May 2018 23:33:26 +0100
From:   "Maciej W. Rozycki" <macro@...s.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        James Hogan <jhogan@...nel.org>
CC:     Ralf Baechle <ralf@...ux-mips.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-mips@...ux-mips.org>,
        <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: [PATCH 2/3] MIPS: Correct the 64-bit DSP accumulator register size

Use the `unsigned long' rather than `__u32' type for DSP accumulator 
registers, like with the regular MIPS multiply/divide accumulator and 
general-purpose registers, as all are 64-bit in 64-bit implementations 
and using a 32-bit data type leads to contents truncation on context 
saving.

Update `arch_ptrace' and `compat_arch_ptrace' accordingly, removing 
casts that are similarly not used with multiply/divide accumulator or 
general-purpose register accesses.

Cc: stable@...r.kernel.org # 2.6.15+
Fixes: e50c0a8fa60d ("Support the MIPS32 / MIPS64 DSP ASE.")
Signed-off-by: Maciej W. Rozycki <macro@...s.com>
---
Hi,

 I have no 64-bit DSP hardware handy to verify this change, however some 
surely exists and is used to run Linux, as indicated by GDB PR gdb/22286, 
<https://sourceware.org/bugzilla/show_bug.cgi?id=22286>, so we better get 
it right before people start screaming.

  Maciej
---
 arch/mips/include/asm/processor.h |    2 +-
 arch/mips/kernel/ptrace.c         |    2 +-
 arch/mips/kernel/ptrace32.c       |    2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

linux-mips-dsp64.diff
Index: linux-jhogan-test/arch/mips/include/asm/processor.h
===================================================================
--- linux-jhogan-test.orig/arch/mips/include/asm/processor.h	2018-03-21 17:13:52.000000000 +0000
+++ linux-jhogan-test/arch/mips/include/asm/processor.h	2018-05-09 22:35:33.248559000 +0100
@@ -141,7 +141,7 @@ struct mips_fpu_struct {
 
 #define NUM_DSP_REGS   6
 
-typedef __u32 dspreg_t;
+typedef unsigned long dspreg_t;
 
 struct mips_dsp_state {
 	dspreg_t	dspr[NUM_DSP_REGS];
Index: linux-jhogan-test/arch/mips/kernel/ptrace.c
===================================================================
--- linux-jhogan-test.orig/arch/mips/kernel/ptrace.c	2018-05-09 22:34:00.000000000 +0100
+++ linux-jhogan-test/arch/mips/kernel/ptrace.c	2018-05-09 22:37:45.416608000 +0100
@@ -856,7 +856,7 @@ long arch_ptrace(struct task_struct *chi
 				goto out;
 			}
 			dregs = __get_dsp_regs(child);
-			tmp = (unsigned long) (dregs[addr - DSP_BASE]);
+			tmp = dregs[addr - DSP_BASE];
 			break;
 		}
 		case DSP_CONTROL:
Index: linux-jhogan-test/arch/mips/kernel/ptrace32.c
===================================================================
--- linux-jhogan-test.orig/arch/mips/kernel/ptrace32.c	2018-03-21 17:13:52.000000000 +0000
+++ linux-jhogan-test/arch/mips/kernel/ptrace32.c	2018-05-09 22:45:50.924418000 +0100
@@ -142,7 +142,7 @@ long compat_arch_ptrace(struct task_stru
 				goto out;
 			}
 			dregs = __get_dsp_regs(child);
-			tmp = (unsigned long) (dregs[addr - DSP_BASE]);
+			tmp = dregs[addr - DSP_BASE];
 			break;
 		}
 		case DSP_CONTROL: