Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762222AbdDSK07 (ORCPT ); Wed, 19 Apr 2017 06:26:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:53984 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1761922AbdDSK0z (ORCPT ); Wed, 19 Apr 2017 06:26:55 -0400 Date: Wed, 19 Apr 2017 12:26:36 +0200 From: Borislav Petkov 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 , "Ravi V. Shankar" , Shuah Khan , linux-kernel@vger.kernel.org, x86@kernel.org, linux-msdos@vger.kernel.org, wine-devel@winehq.org, Adam Buchbinder , Colin Ian King , Lorenzo Stoakes , Qiaowei Ren , Arnaldo Carvalho de Melo , Adrian Hunter , Kees Cook , Thomas Garnier , Dmitry Vyukov Subject: Re: [v6 PATCH 07/21] x86/insn-eval: Add utility function to get segment descriptor Message-ID: <20170419102636.chx5fwofysehy3yx@pd.tnic> References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> <20170308003254.27833-8-ricardo.neri-calderon@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170308003254.27833-8-ricardo.neri-calderon@linux.intel.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4518 Lines: 145 On Tue, Mar 07, 2017 at 04:32:40PM -0800, Ricardo Neri wrote: > The segment descriptor contains information that is relevant to how linear > address need to be computed. It contains the default size of addresses as > well as the base address of the segment. Thus, given a segment selector, > we ought look at segment descriptor to correctly calculate the linear > address. > > In protected mode, the segment selector might indicate a segment > descriptor from either the global descriptor table or a local descriptor > table. Both cases are considered in this function. > > This function is the initial implementation for subsequent functions that > will obtain the aforementioned attributes of the segment descriptor. > > 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/lib/insn-eval.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 61 insertions(+) > > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c > index 8d45df8..8608adf 100644 > --- a/arch/x86/lib/insn-eval.c > +++ b/arch/x86/lib/insn-eval.c > @@ -5,9 +5,13 @@ > */ > #include > #include > +#include > +#include > #include > #include > #include > +#include > +#include > #include > > enum reg_type { > @@ -294,6 +298,63 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, > } > > /** > + * get_desc() - Obtain address of segment descriptor > + * @seg: Segment selector Maybe that should be @sel if it is a sel-ector. :) And using "sel" makes more sense then when you look at: desc_base = sel & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK); for example: > + * @desc: Pointer to the selected segment descriptor > + * > + * Given a segment selector, obtain a memory pointer to the segment s/memory // > + * descriptor. Both global and local descriptor tables are supported. > + * desc will contain the address of the descriptor. > + * > + * Return: 0 if success, -EINVAL if failure Why isn't this function returning the pointer or NULL on error? Maybe the later patches have an answer and I'll discover it if I continue reviewing :) > + */ > +static int get_desc(unsigned short seg, struct desc_struct **desc) > +{ > + struct desc_ptr gdt_desc = {0, 0}; > + unsigned long desc_base; > + > + if (!desc) > + return -EINVAL; > + > + desc_base = seg & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK); That looks useless as you're doing it below again. > + > +#ifdef CONFIG_MODIFY_LDT_SYSCALL > + if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { > + seg >>= 3; > + > + mutex_lock(¤t->active_mm->context.lock); > + if (unlikely(!current->active_mm->context.ldt || Is that really a fast path to complicate the if-test with an unlikely()? If not, you don't really need it. > + seg >= current->active_mm->context.ldt->size)) { ldt->size is the size of the descriptor table but you've shifted seg by 3. That selector index is shifted by 3 (to the left) to form an offset into the descriptor table because the entries there are 8 bytes. So I *think* you wanna use the "useless" desc_base above... :) > + *desc = NULL; > + mutex_unlock(¤t->active_mm->context.lock); > + return -EINVAL; > + } > + > + *desc = ¤t->active_mm->context.ldt->entries[seg]; ... and seg here as it is an index into the table. > + mutex_unlock(¤t->active_mm->context.lock); > + return 0; > + } > +#endif > + native_store_gdt(&gdt_desc); > + > + /* > + * Bits [15:3] of the segment selector contain the index. Such > + * index needs to be multiplied by 8. ... because . -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --