From mboxrd@z Thu Jan 1 00:00:00 1970 From: Borislav Petkov Subject: Re: [v6 PATCH 09/21] x86/insn-eval: Add functions to get default operand and address sizes Date: Thu, 20 Apr 2017 15:06:49 +0200 Message-ID: <20170420130649.ezudk44ckddznadu@pd.tnic> References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> <20170308003254.27833-10-ricardo.neri-calderon@linux.intel.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <20170308003254.27833-10-ricardo.neri-calderon@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="utf-8" To: Ricardo Neri Cc: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Andrew Morton , Brian Gerst , Chris Metcalf , Dave Hansen , Paolo Bonzini , Masami Hiramatsu , Huang Rui , Jiri Slaby , Jonathan Corbet , "Michael S. Tsirkin" , Paul Gortmaker , Vlastimil Babka , Chen Yucong , Alexandre Julliard , Stas Sergeev , Fenghua Yu On Tue, Mar 07, 2017 at 04:32:42PM -0800, Ricardo Neri wrote: > These functions read the default values of the address and operand sizes > as specified in the segment descriptor. This information is determined > from the D and L bits. Hence, it can be used for both IA-32e 64-bit and > 32-bit legacy modes. For virtual-8086 mode, the default address and > operand sizes are always 2 bytes. Yeah, we tend to call that customarily 16-bit :) > The D bit is only meaningful for code segments. Thus, these functions > always use the code segment selector contained in regs. > > Cc: Dave Hansen > Cc: Adam Buchbinder > Cc: Colin Ian King > Cc: Lorenzo Stoakes > Cc: Qiaowei Ren > Cc: Arnaldo Carvalho de Melo > Cc: Masami Hiramatsu > Cc: Adrian Hunter > Cc: Kees Cook > Cc: Thomas Garnier > Cc: Peter Zijlstra > Cc: Borislav Petkov > Cc: Dmitry Vyukov > Cc: Ravi V. Shankar > Cc: x86@kernel.org > Signed-off-by: Ricardo Neri > --- > arch/x86/include/asm/insn-eval.h | 2 + > arch/x86/lib/insn-eval.c | 80 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 82 insertions(+) > > diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h > index b201742..a0d81fc 100644 > --- a/arch/x86/include/asm/insn-eval.h > +++ b/arch/x86/include/asm/insn-eval.h > @@ -15,6 +15,8 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs); > int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs); > int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs); > int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs); > +unsigned char insn_get_seg_default_address_bytes(struct pt_regs *regs); > +unsigned char insn_get_seg_default_operand_bytes(struct pt_regs *regs); > unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn, > int regoff, bool use_default_seg); > > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c > index 383ca83..cda6c71 100644 > --- a/arch/x86/lib/insn-eval.c > +++ b/arch/x86/lib/insn-eval.c > @@ -421,6 +421,86 @@ unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn, > } > > /** > + * insn_get_seg_default_address_bytes - Obtain default address size of segment > + * @regs: Set of registers containing the segment selector > + * > + * Obtain the default address size as indicated in the segment descriptor > + * selected in regs' code segment selector. In protected mode, the default > + * address is determined by inspecting the L and D bits of the segment > + * descriptor. In virtual-8086 mode, the default is always two bytes. > + * > + * Return: Default address size of segment 0 on error. > + */ > +unsigned char insn_get_seg_default_address_bytes(struct pt_regs *regs) > +{ > + struct desc_struct *desc; > + unsigned short seg; > + int ret; > + > + if (v8086_mode(regs)) > + return 2; > + > + seg = (unsigned short)regs->cs; > + > + ret = get_desc(seg, &desc); > + if (ret) > + return 0; > + > + switch ((desc->l << 1) | desc->d) { > + case 0: /* Legacy mode. 16-bit addresses. CS.L=0, CS.D=0 */ > + return 2; > + case 1: /* Legacy mode. 32-bit addresses. CS.L=0, CS.D=1 */ > + return 4; > + case 2: /* IA-32e 64-bit mode. 64-bit addresses. CS.L=1, CS.D=0 */ > + return 8; > + case 3: /* Invalid setting. CS.L=1, CS.D=1 */ > + /* fall through */ > + default: > + return 0; > + } > +} > + > +/** > + * insn_get_seg_default_operand_bytes - Obtain default operand size of segment > + * @regs: Set of registers containing the segment selector > + * > + * Obtain the default operand size as indicated in the segment descriptor > + * selected in regs' code segment selector. In protected mode, the default > + * operand size is determined by inspecting the L and D bits of the segment > + * descriptor. In virtual-8086 mode, the default is always two bytes. > + * > + * Return: Default operand size of segment > + */ > +unsigned char insn_get_seg_default_operand_bytes(struct pt_regs *regs) Right, so default address and operand size always go together so I don't think you need two separate functions. So what I'd suggest - provided this pans out (I still haven't reviewed the whole thing) - is to determine the operating mode of the segment: long, legacy, etc and then return both address and operand sizes. Patch 17/21 needs them both at the same time AFAICT. -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --