Messages in this thread Patch in this message | | | Date | Sat, 23 Oct 2021 19:32:34 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH 2/3] x86/insn-eval: Introduce insn_decode_mmio() |
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On Tue, Oct 19, 2021 at 10:34:45AM +0200, Peter Zijlstra wrote: > On Mon, Oct 18, 2021 at 07:49:41PM +0300, Kirill A. Shutemov wrote: > > On Mon, Oct 18, 2021 at 05:53:49PM +0200, Peter Zijlstra wrote: > > > On Mon, Oct 18, 2021 at 06:33:32PM +0300, Kirill A. Shutemov wrote: > > > > > > > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c > > > > index fbaa3fa24bde..2ab29d8d6731 100644 > > > > --- a/arch/x86/lib/insn-eval.c > > > > +++ b/arch/x86/lib/insn-eval.c > > > > @@ -1559,3 +1559,85 @@ bool insn_decode_from_regs(struct insn *insn, struct pt_regs *regs, > > > > > > > > return true; > > > > } > > > > + > > > > +/** > > > > + * insn_decode_mmio() - Decode a MMIO instruction > > > > + * @insn: Structure to store decoded instruction > > > > + * @bytes: Returns size of memory operand > > > > + * > > > > + * Decodes instruction that used for Memory-mapped I/O. > > > > + * > > > > + * Returns: > > > > + * > > > > + * Type of the instruction. Size of the memory operand is stored in > > > > + * @bytes. If decode failed, MMIO_DECODE_FAILED returned. > > > > + */ > > > > +enum mmio_type insn_decode_mmio(struct insn *insn, int *bytes) > > > > +{ > > > > + int type = MMIO_DECODE_FAILED; > > > > + > > > > + *bytes = 0; > > > > + > > > > + insn_get_opcode(insn); > > > > > > insn_get_opcode() can fail. Either you assume it's already called and > > > don't call it, or you can't assume anything and get to do error > > > handling. > > > > Fair enough. I will return MMIO_DECODE_FAILED if insn_get_opcode() fails. > > > > BTW, looks like is_string_insn() suffers from the same issue. Not sure how > > to fix it though. > > AFAICT all callers of insn_get_addr_ref() (which is what > is_string_insn() seems to be part of) do a insn_decode_*() call with > error checking before. > > So it looks like that insn_get_opcode() in there is superfluous. > probably same for insn_has_rep_prefix() / get_seg_reg_override_idx() / > get_eff_addr_modrm_*(). That all wants cleaning up. > > The esaiest way is probably to push those things up the callchains into > the !static function and have it fail early there.
Looks like insn_get_addr_ref() is the only non-static callsite:
is_string_insn check_seg_overrides resolve_seg_reg get_seg_base_limit get_addr_ref_XX insn_get_addr_ref resolve_default_seg resolve_seg_reg (as above)
What about this:
From 576a390de4759f591709c9961b5d7add02c814f0 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Date: Sat, 23 Oct 2021 19:26:07 +0300 Subject: [PATCH] x86/insn-eval: Handle insn_get_opcode() failure
is_string_insn() calls insn_get_opcode() that can fail, but does not handle the failure.
is_string_insn() interface does not allow to communicate an error to the caller.
Push insn_get_opcode() to the only non-static user of is_string_insn() and fail it early if insn_get_opcode() fails.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- arch/x86/lib/insn-eval.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 1714359f48bd..ccbc7b253d98 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -37,8 +37,6 @@ enum reg_type { */ static bool is_string_insn(struct insn *insn) { - insn_get_opcode(insn); - /* All string instructions have a 1-byte opcode. */ if (insn->opcode.nbytes != 1) return false; @@ -1425,6 +1423,9 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) if (!insn || !regs) return (void __user *)-1L; + if (insn_get_opcode(insn)) + return (void __user *)-1L; + switch (insn->addr_bytes) { case 2: return get_addr_ref_16(insn, regs); -- Kirill A. Shutemov
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