Re: [PATCH 4/5] MIPS: Execute any partial write of the last register with PTRACE_SETREGSET
From: Dave Martin <Dave.Martin@arm.com>
Date: 2017-11-30 17:28:46
Also in:
lkml, stable
On Wed, Nov 29, 2017 at 03:21:14PM +0000, Maciej W. Rozycki wrote:
quoted hunk ↗ jump to hunk
Fix a commit d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") bug and allow the last register requested with a ptrace(2) PTRACE_SETREGSET call to be partially written if supplied this way by the caller, like with other register sets. Cc: stable@vger.kernel.org # v4.11+ Fixes: d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") Signed-off-by: Maciej W. Rozycki <redacted> --- arch/mips/kernel/ptrace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) linux-mips-nt-prfpreg-count.diff Index: linux-sfr-test/arch/mips/kernel/ptrace.c ===================================================================--- linux-sfr-test.orig/arch/mips/kernel/ptrace.c 2017-11-21 22:12:00.000000000 +0000 +++ linux-sfr-test/arch/mips/kernel/ptrace.c 2017-11-21 22:13:13.471970000 +0000@@ -484,7 +484,7 @@ static int fpr_set_msa(struct task_struc int err; BUILD_BUG_ON(sizeof(fpr_val) != sizeof(elf_fpreg_t)); - for (i = 0; i < NUM_FPU_REGS && *count >= sizeof(elf_fpreg_t); i++) { + for (i = 0; i < NUM_FPU_REGS && *count > 0; i++) { err = user_regset_copyin(pos, count, kbuf, ubuf, &fpr_val, i * sizeof(elf_fpreg_t), (i + 1) * sizeof(elf_fpreg_t));
But mips*_regsets[REGSET_FPR].size == sizeof(elf_fpreg_t), linux/kernel/regset.c:ptrace_regset() polices iov_len % regset->size == 0, and each user_regset_copyout() call here transfers sizeof(elf_fpreg_t) bytes, decrementing *count by that amount unless something goest wrong in which case we return. So how do we end up with *count > 0 && *count < sizeof(elf_fpreg_t) here? If we can't end up with that, then this patch doesn't change ABI- observable behaviour, unless I've missed something. If we can end up with that somehow, then this patch reintroduces the issue d614fd58a283 aims to fix, whereby fpr_val can contain uninitialised kernel stack which userspace can then obtain via PTRACE_GETREGSET. Cheers ---Dave