MIPS: ptrace: expose FIR register through FP regset
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Message ID
State Accepted
Delegated to: James Hogan
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Series
  • MIPS: ptrace: expose FIR register through FP regset
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Commit Message

Maciej W. Rozycki April 30, 2018, 2:56 p.m. UTC 
Correct commit 7aeb753b5353 ("MIPS: Implement task_user_regset_view.") 
and expose the FIR register using the unused 4 bytes at the end of the 
NT_PRFPREG regset.  Without that register included clients cannot use 
the PTRACE_GETREGSET request to retrieve the complete FPU register set
and have to resort to one of the older interfaces, either PTRACE_PEEKUSR 
or PTRACE_GETFPREGS, to retrieve the missing piece of data.  Also the 
register is irreversibly missing from core dumps.

This register is architecturally hardwired and read-only so the write
path does not matter.  Ignore data supplied on writes then.

Cc:  # v3.13+
Fixes: 7aeb753b5353 ("MIPS: Implement task_user_regset_view.")
Signed-off-by: James Hogan <>
Signed-off-by: Maciej W. Rozycki <>
---
 arch/mips/kernel/ptrace.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

linux-mips-nt-prfpreg-fir.diff

Comments

James Hogan May 11, 2018, 10:17 p.m. UTC | #1 
On Mon, Apr 30, 2018 at 03:56:47PM +0100, Maciej W. Rozycki wrote:
> Correct commit 7aeb753b5353 ("MIPS: Implement task_user_regset_view.") 
> and expose the FIR register using the unused 4 bytes at the end of the 
> NT_PRFPREG regset.  Without that register included clients cannot use 
> the PTRACE_GETREGSET request to retrieve the complete FPU register set
> and have to resort to one of the older interfaces, either PTRACE_PEEKUSR 
> or PTRACE_GETFPREGS, to retrieve the missing piece of data.  Also the 
> register is irreversibly missing from core dumps.
> 
> This register is architecturally hardwired and read-only so the write
> path does not matter.  Ignore data supplied on writes then.
> 
> Cc:  # v3.13+
> Fixes: 7aeb753b5353 ("MIPS: Implement task_user_regset_view.")
> Signed-off-by: James Hogan <>
> Signed-off-by: Maciej W. Rozycki <>

Looks good, applied for 4.17.

Thanks for cleaning & submitting this :)

Cheers
James

Patch
diff mbox series 

Index: linux-sfr-test/arch/mips/kernel/ptrace.c
===================================================================
--- linux-sfr-test.orig/arch/mips/kernel/ptrace.c	:22:17. +0000
+++ linux-sfr-test/arch/mips/kernel/ptrace.c	:22: +0000
@@ -454,7 +454,7 @@  static int fpr_get_msa(struct task_struc
 /*
  * Copy the floating-point context to the supplied NT_PRFPREG buffer.
  * Choose the appropriate helper for general registers, and then copy
- * the FCSR register separately.
+ * the FCSR and FIR registers separately.
  */
 static int fpr_get(struct task_struct *target,
 		   const struct user_regset *regset,
@@ -462,6 +462,7 @@  static int fpr_get(struct task_struct *t
 		   void *kbuf, void __user *ubuf)
 {
 	const int fcr31_pos = NUM_FPU_REGS * sizeof(elf_fpreg_t);
+	const int fir_pos = fcr31_pos + sizeof(u32);
 	int err;
 
 	if (sizeof(target->thread.fpu.fpr[0]) == sizeof(elf_fpreg_t))
@@ -474,6 +475,12 @@  static int fpr_get(struct task_struct *t
 	err = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
 				  &target->thread.fpu.fcr31,
 				  fcr31_pos, fcr31_pos + sizeof(u32));
+	if (err)
+		return err;
+
+	err = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
+				  &boot_cpu_data.fpu_id,
+				  fir_pos, fir_pos + sizeof(u32));
 
 	return err;
 }
@@ -522,7 +529,8 @@  static int fpr_set_msa(struct task_struc
 /*
  * Copy the supplied NT_PRFPREG buffer to the floating-point context.
  * Choose the appropriate helper for general registers, and then copy
- * the FCSR register separately.
+ * the FCSR register separately.  Ignore the incoming FIR register
+ * contents though, as the register is read-only.
  *
  * We optimize for the case where `count % sizeof(elf_fpreg_t) == 0',
  * which is supposed to have been guaranteed by the kernel before
@@ -536,6 +544,7 @@  static int fpr_set(struct task_struct *t
 		   const void *kbuf, const void __user *ubuf)
 {
 	const int fcr31_pos = NUM_FPU_REGS * sizeof(elf_fpreg_t);
+	const int fir_pos = fcr31_pos + sizeof(u32);
 	u32 fcr31;
 	int err;
 
@@ -563,6 +572,11 @@  static int fpr_set(struct task_struct *t
 		ptrace_setfcr31(target, fcr31);
 	}
 
+	if (count > 0)
+		err = user_regset_copyin_ignore(&pos, &count, &kbuf, &ubuf,
+						fir_pos,
+						fir_pos + sizeof(u32));
+
 	return err;
 }