(2015/01/28 9:06), Andy Lutomirski wrote: > x86 instructions cannot exceed 15 bytes, and the instruction decoder > should enforce that. Prior to 6ba48ff46f76, the instruction length > limit was implicitly set to 16, which was an approximation of 15, > but there is currently no limit at all. > > Fix MAX_INSN_SIZE (it should be 15, not 16), and fix the decoder to > reject instructions that exceed MAX_INSN_SIZE. > > Other than potentially confusing some of the decoder sanity checks, > I'm not aware of any actual problems that omitting this check would > cause, nor am I aware of any practical problems caused by the > MAX_INSN_SIZE error. >
Thank you for updating. This looks good to me :) Acked-by: Masami Hiramatsu <[email protected]> Ingo, could you pull this in -tip tree? Thank you, > Fixes: 6ba48ff46f76 x86: Remove arbitrary instruction size limit in > instruction decoder > Cc: Masami Hiramatsu <[email protected]> > Signed-off-by: Andy Lutomirski <[email protected]> > --- > > Changes from old versions: folded > > arch/x86/include/asm/insn.h | 2 +- > arch/x86/lib/insn.c | 7 +++++++ > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h > index 47f29b1d1846..e7814b74caf8 100644 > --- a/arch/x86/include/asm/insn.h > +++ b/arch/x86/include/asm/insn.h > @@ -69,7 +69,7 @@ struct insn { > const insn_byte_t *next_byte; > }; > > -#define MAX_INSN_SIZE 16 > +#define MAX_INSN_SIZE 15 > > #define X86_MODRM_MOD(modrm) (((modrm) & 0xc0) >> 6) > #define X86_MODRM_REG(modrm) (((modrm) & 0x38) >> 3) > diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c > index 2480978b31cc..bf1f227cf706 100644 > --- a/arch/x86/lib/insn.c > +++ b/arch/x86/lib/insn.c > @@ -52,6 +52,13 @@ > */ > void insn_init(struct insn *insn, const void *kaddr, int buf_len, int x86_64) > { > + /* > + * Instructions longer than MAX_INSN_SIZE (15 bytes) are invalid > + * even if the input buffer is long enough to hold them. > + */ > + if (buf_len > MAX_INSN_SIZE) > + buf_len = MAX_INSN_SIZE; > + > memset(insn, 0, sizeof(*insn)); > insn->kaddr = kaddr; > insn->end_kaddr = kaddr + buf_len; > -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
