Re: [PATCH v2] powerpc/uprobes: Validation for prefixed instruction

On 02/04, Ravi Bangoria wrote:

+static int get_instr(struct mm_struct *mm, unsigned long addr, u32 *instr)
+{
+	struct page *page;
+	struct vm_area_struct *vma;
+	void *kaddr;
+	unsigned int gup_flags = FOLL_FORCE | FOLL_SPLIT_PMD;
+
+	if (get_user_pages_remote(mm, addr, 1, gup_flags, &page, &vma, NULL) <= 0)
+		return -EINVAL;

"vma" is not used, and I don't think you need FOLL_SPLIT_PMD.

Otherwise I can't really comment this ppc-specific change.

To be honest, I don't even understand why do we need this fix. Sure, the
breakpoint in the middle of 64-bit insn won't work, why do we care? The
user should know what does he do.

Not to mention we can't really trust get_user_pages() in that this page
can be modified by mm owner or debugger...

But I won't argue.

Oleg.