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MIPS: Guard against any partial write attempt with PTRACE_SETREGSET

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Complement commit d614fd58a2 ("mips/ptrace: Preserve previous
registers for short regset write") and ensure that no partial register
write attempt is made with PTRACE_SETREGSET, as we do not preinitialize
any temporaries used to hold incoming register data and consequently
random data could be written.

It is the responsibility of the caller, such as `ptrace_regset', to
arrange for writes to span whole registers only, so here we only assert
that it has indeed happened.

Signed-off-by: Maciej W. Rozycki <macro@mips.com>
Fixes: 72b22bbad1 ("MIPS: Don't assume 64-bit FP registers for FP regset")
Cc: James Hogan <james.hogan@mips.com>
Cc: Paul Burton <Paul.Burton@mips.com>
Cc: Alex Smith <alex@alex-smith.me.uk>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # v3.15+
Patchwork: https://patchwork.linux-mips.org/patch/17926/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Maciej W. Rozycki 2017-12-11 22:52:15 +00:00 committed by Ralf Baechle
parent a03fe72572
commit dc24d0edf3
1 changed files with 11 additions and 1 deletions
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12
arch/mips/kernel/ptrace.c
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@ -516,7 +516,15 @@ static int fpr_set_msa(struct task_struct *target,
return 0;
}
/* Copy the supplied NT_PRFPREG buffer to the floating-point context. */
/*
* Copy the supplied NT_PRFPREG buffer to the floating-point context.
*
* We optimize for the case where `count % sizeof(elf_fpreg_t) == 0',
* which is supposed to have been guaranteed by the kernel before
* calling us, e.g. in `ptrace_regset'. We enforce that requirement,
* so that we can safely avoid preinitializing temporaries for
* partial register writes.
*/
static int fpr_set(struct task_struct *target,
const struct user_regset *regset,
unsigned int pos, unsigned int count,
@ -524,6 +532,8 @@ static int fpr_set(struct task_struct *target,
{
int err;
BUG_ON(count % sizeof(elf_fpreg_t));
/* XXX fcr31 */
init_fp_ctx(target);