Messages in this thread | | | Date | Tue, 7 Apr 2020 10:01:04 -0700 | From | Kees Cook <> | Subject | Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation |
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On Tue, Apr 07, 2020 at 01:02:40PM +0200, Peter Zijlstra wrote: > Since we now have infrastructure to analyze module text, disallow > modules that write to CRn and DRn registers. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > arch/x86/kernel/module.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > --- a/arch/x86/kernel/module.c > +++ b/arch/x86/kernel/module.c > @@ -266,6 +266,22 @@ static bool insn_is_vmx(struct insn *ins > return false; > } > > +static bool insn_is_mov_CRn(struct insn *insn) > +{ > + if (insn->opcode.bytes[0] == 0x0f && insn->opcode.bytes[1] == 0x22) > + return true;
I always cringe at numeric literals. Would it be overkill to add defines for these (and the others that have comments next to them in 3/4)? It makes stuff easier to grep, etc. (e.g. we have register names in arch/x86/include/asm/asm.h, do we need instruction names somewhere else? I assume objtool has a bunch of this too...)
-Kees
> + > + return false; > +} > + > +static bool insn_is_mov_DRn(struct insn *insn) > +{ > + if (insn->opcode.bytes[0] == 0x0f && insn->opcode.bytes[1] == 0x23) > + return true; > + > + return false; > +} > + > static int decode_module(struct module *mod, void *text, void *text_end, bool sld_safe) > { > bool allow_vmx = sld_safe || !split_lock_enabled(); > @@ -285,6 +301,11 @@ static int decode_module(struct module * > return -ENOEXEC; > } > > + if (insn_is_mov_CRn(&insn) || insn_is_mov_DRn(&insn)) { > + pr_err("Module writes to CRn or DRn, please use the proper accessors: %s\n", mod->name); > + return -ENOEXEC; > + } > + > text += insn.length; > } > > >
-- Kees Cook
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