Messages in this thread |  | | Subject | Re: [PATCH v2] powerpc/uprobes: Validation for prefixed instruction | From | Ravi Bangoria <> | Date | Mon, 8 Feb 2021 16:43:14 +0530 |
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On 2/4/21 6:38 PM, Naveen N. Rao wrote: > 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.bangoria@linux.ibm.com> >> --- >> v1: http://lore.kernel.org/r/20210119091234.76317-1-ravi.bangoria@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 <ananth@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)
Ok.
> > 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;
Yeah this is better.
Thanks for the review, Naveen! Ravi
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