[PATCH 3.16 306/366] MIPS: ptrace: Expose FIR register through FP regset

Ben Hutchings
2018-10-14T23:11:48Z

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

commit 71e909c0cdad28a1df1fa14442929e68615dee45 upstream.

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.

Fixes: 7aeb753b5353 ("MIPS: Implement task_user_regset_view.")
Signed-off-by: James Hogan <jhogan@kernel.org>
Signed-off-by: Maciej W. Rozycki <macro@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/19273/
Signed-off-by: James Hogan <jhogan@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/mips/kernel/ptrace.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -481,7 +481,7 @@ 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,
@@ -489,6 +489,7 @@ 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))
@@ -501,6 +502,12 @@ 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;
}
@@ -549,7 +556,8 @@ 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
@@ -563,6 +571,7 @@ 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;

@@ -590,6 +599,11 @@ 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;
}