On 2021/02/04 04:17PM, Ravi Bangoria wrote: > Don't allow Uprobe on 2nd word of a prefixed instruction. As per > ISA 3.1, prefixed instruction should not cross 64-byte boundary. > So don't allow Uprobe on such prefixed instruction as well. > > There are two ways probed instruction is changed in mapped pages. > First, when Uprobe is activated, it searches for all the relevant > pages and replace instruction in them. In this case, if we notice > that probe is on the 2nd word of prefixed instruction, error out > directly. Second, when Uprobe is already active and user maps a > relevant page via mmap(), instruction is replaced via mmap() code > path. But because Uprobe is invalid, entire mmap() operation can > not be stopped. In this case just print an error and continue. > > Signed-off-by: Ravi Bangoria <ravi.bango...@linux.ibm.com> > --- > v1: > http://lore.kernel.org/r/20210119091234.76317-1-ravi.bango...@linux.ibm.com > v1->v2: > - Instead of introducing new arch hook from verify_opcode(), use > existing hook arch_uprobe_analyze_insn(). > - Add explicit check for prefixed instruction crossing 64-byte > boundary. If probe is on such instruction, throw an error. > > arch/powerpc/kernel/uprobes.c | 66 ++++++++++++++++++++++++++++++++++- > 1 file changed, 65 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c > index e8a63713e655..485d19a2a31f 100644 > --- a/arch/powerpc/kernel/uprobes.c > +++ b/arch/powerpc/kernel/uprobes.c > @@ -7,6 +7,7 @@ > * Adapted from the x86 port by Ananth N Mavinakayanahalli > <ana...@in.ibm.com> > */ > #include <linux/kernel.h> > +#include <linux/highmem.h> > #include <linux/sched.h> > #include <linux/ptrace.h> > #include <linux/uprobes.h> > @@ -28,6 +29,69 @@ bool is_trap_insn(uprobe_opcode_t *insn) > return (is_trap(*insn)); > } > > +#ifdef CONFIG_PPC64 > +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; > + > + kaddr = kmap_atomic(page); > + *instr = *((u32 *)(kaddr + (addr & ~PAGE_MASK))); > + kunmap_atomic(kaddr); > + put_page(page); > + return 0; > +} > + > +static int validate_prefixed_instr(struct mm_struct *mm, unsigned long addr) > +{ > + struct ppc_inst inst; > + u32 prefix, suffix; > + > + /* > + * No need to check if addr is pointing to beginning of the > + * page. Even if probe is on a suffix of page-unaligned > + * prefixed instruction, hw will raise exception and kernel > + * will send SIGBUS. > + */ > + if (!(addr & ~PAGE_MASK)) > + return 0; > + > + if (get_instr(mm, addr, &prefix) < 0) > + return -EINVAL; > + if (get_instr(mm, addr + 4, &suffix) < 0) > + return -EINVAL; > + > + inst = ppc_inst_prefix(prefix, suffix); > + if (ppc_inst_prefixed(inst) && (addr & 0x3F) == 0x3C) { > + printk_ratelimited("Cannot register a uprobe on 64 byte " ^^^^^^^^^^^^^^^^^^ pr_info_ratelimited()
It should be sufficient to check the primary opcode to determine if it is a prefixed instruction. You don't have to read the suffix. I see that we don't have a helper to do this currently, so you could do: if (ppc_inst_primary_opcode(ppc_inst(prefix)) == 1) In the future, it might be worthwhile to add IS_PREFIX() as a macro similar to IS_MTMSRD() if there are more such uses. Along with this, if you also add the below to the start of this function, you can get rid of the #ifdef: if (!IS_ENABLED(CONFIG_PPC64)) return 0; - Naveen