From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: Borislav Petkov <bp@suse.de>
Cc: Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Brian Gerst <brgerst@gmail.com>,
Chris Metcalf <cmetcalf@mellanox.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Huang Rui <ray.huang@amd.com>, Jiri Slaby <jslaby@suse.cz>,
Jonathan Corbet <corbet@lwn.net>,
"Michael S. Tsirkin" <mst@redhat.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Vlastimil Babka <vbabka@suse.cz>, Chen Yucong <slaoub@gmail.com>,
Alexandre Julliard <julliard@winehq.org>,
Stas Sergeev <stsp@list.ru>, Fenghua Yu <fenghua.yu@intel.com>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Shuah Khan <shuah@kernel.org>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-msdos@vger.kernel.org, wine-devel@winehq.org,
Adam Buchbinder <adam.buchbinder@gmail.com>,
Colin Ian King <colin.king@canonical.com>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Qiaowei Ren <qiaowei.ren@intel.com>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Adrian Hunter <adrian.hunter@intel.com>,
Kees Cook <keescook@chromium.org>,
Thomas Garnier <thgarnie@google.com>,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [v6 PATCH 10/21] x86/insn-eval: Do not use R/EBP as base if mod in ModRM is zero
Date: Wed, 26 Apr 2017 18:29:59 -0700 [thread overview]
Message-ID: <1493256599.36058.83.camel@ranerica-desktop> (raw)
In-Reply-To: <20170421105258.q4vqrephtm7t3h4c@pd.tnic>
On Fri, 2017-04-21 at 12:52 +0200, Borislav Petkov wrote:
> On Tue, Mar 07, 2017 at 04:32:43PM -0800, Ricardo Neri wrote:
> > Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software
> > Developer's Manual volume 2A states that when the mod part of the ModRM
> > byte is zero and R/EBP is specified in the R/M part of such bit, the value
> > of the aforementioned register should not be used in the address
> > computation. Instead, a 32-bit displacement is expected. The instruction
> > decoder takes care of setting the displacement to the expected value.
> > Returning -EDOM signals callers that they should ignore the value of such
> > register when computing the address encoded in the instruction operands.
> >
> > Also, callers should exercise care to correctly interpret this particular
> > case. In IA-32e 64-bit mode, the address is given by the displacement plus
> > the value of the RIP. In IA-32e compatibility mode, the value of EIP is
> > ignored. This correction is done for our insn_get_addr_ref.
> >
> > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
> > Cc: Colin Ian King <colin.king@canonical.com>
> > Cc: Lorenzo Stoakes <lstoakes@gmail.com>
> > Cc: Qiaowei Ren <qiaowei.ren@intel.com>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Cc: Masami Hiramatsu <mhiramat@kernel.org>
> > Cc: Adrian Hunter <adrian.hunter@intel.com>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Thomas Garnier <thgarnie@google.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Borislav Petkov <bp@suse.de>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
> > Cc: x86@kernel.org
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> > ---
> > arch/x86/lib/insn-eval.c | 25 +++++++++++++++++++++++--
> > 1 file changed, 23 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
> > index cda6c71..ea10b03 100644
> > --- a/arch/x86/lib/insn-eval.c
> > +++ b/arch/x86/lib/insn-eval.c
> > @@ -250,6 +250,14 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
> > switch (type) {
> > case REG_TYPE_RM:
> > regno = X86_MODRM_RM(insn->modrm.value);
> > + /* if mod=0, register R/EBP is not used in the address
> > + * computation. Instead, a 32-bit displacement is expected;
> > + * the instruction decoder takes care of reading such
> > + * displacement. This is true for both R/EBP and R13, as the
> > + * REX.B bit is not decoded.
> > + */
>
> I'd simply write here: "ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit
> displacement is following."
I will shorten the comment.
>
> In addition, kernel comments style is:
>
> /*
> * A sentence ending with a full-stop.
> * Another sentence. ...
> * More sentences. ...
> */
... and use the correct style. I feel bad I missed this one.
>
> > + if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
> > + return -EDOM;
>
> if (X86_MODRM_MOD(insn->modrm.value) == 0 &&
> X86_MODRM_RM(insn->modrm.value) == 5)
>
> looks more understandable to me.
Should I go with !(X86_MODRM_MOD(insn->modrm.value)) as you suggested in
other patches?
>
> > if (X86_REX_B(insn->rex_prefix.value))
> > regno += 8;
> > break;
> > @@ -599,9 +607,22 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
> > eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
> > } else {
> > addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
> > - if (addr_offset < 0)
> > + /* -EDOM means that we must ignore the address_offset.
> > + * The only case in which we see this value is when
> > + * R/M points to R/EBP. In such a case, in 64-bit mode
> > + * the effective address is relative to tho RIP.
>
> s/tho//
Will correct.
>
> > + */
>
> Kernel comments style is:
>
> /*
> * A sentence ending with a full-stop.
> * Another sentence. ...
> * More sentences. ...
> */
>
Will correct.
> > + if (addr_offset == -EDOM) {
> > + eff_addr = 0;
> > +#ifdef CONFIG_X86_64
> > + if (user_64bit_mode(regs))
> > + eff_addr = (long)regs->ip;
>
> Is regs->ip the rIP of the *following* insn?
No this is a bug. This should be regs->ip + insn.length.
>
> > +#endif
>
> You can do this in a prepatch and then get rid of the ifdeffery here:
>
> diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
> index 2b5d686ea9f3..f6239273c5f1 100644
> --- a/arch/x86/include/asm/ptrace.h
> +++ b/arch/x86/include/asm/ptrace.h
> @@ -115,9 +115,9 @@ static inline int v8086_mode(struct pt_regs *regs)
> #endif
> }
>
> -#ifdef CONFIG_X86_64
> static inline bool user_64bit_mode(struct pt_regs *regs)
> {
> +#ifdef CONFIG_X86_64
> #ifndef CONFIG_PARAVIRT
> /*
> * On non-paravirt systems, this is the only long mode CPL 3
> @@ -128,6 +128,9 @@ static inline bool user_64bit_mode(struct pt_regs *regs)
> /* Headers are too twisted for this to go in paravirt.h. */
> return regs->cs == __USER_CS || regs->cs == pv_info.extra_user_64bit_cs;
> #endif
> +#else /* !CONFIG_X86_64 */
> + return false;
> +#endif
> }
This look nice. I will add this pre-patch.
Thanks and BR,
Ricardo
next prev parent reply other threads:[~2017-04-27 1:30 UTC|newest]
Thread overview: 112+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-08 0:32 [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 01/21] x86/mpx: Use signed variables to compute effective addresses Ricardo Neri
2017-04-11 21:56 ` Borislav Petkov
2017-04-26 1:40 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 02/21] x86/mpx: Do not use SIB index if index points to R/ESP Ricardo Neri
2017-04-11 11:31 ` Borislav Petkov
2017-04-26 1:39 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 03/21] x86/mpx: Do not use R/EBP as base in the SIB byte with Mod = 0 Ricardo Neri
2017-04-11 22:08 ` Borislav Petkov
2017-04-26 2:04 ` Ricardo Neri
2017-04-26 8:05 ` Borislav Petkov
2017-04-27 22:49 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 04/21] x86/mpx, x86/insn: Relocate insn util functions to a new insn-kernel Ricardo Neri
2017-04-12 10:03 ` Borislav Petkov
2017-04-26 2:05 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 05/21] x86/insn-eval: Add utility functions to get register offsets Ricardo Neri
2017-04-12 16:28 ` Borislav Petkov
2017-04-26 18:13 ` Ricardo Neri
2017-04-28 10:40 ` Borislav Petkov
2017-03-08 0:32 ` [v6 PATCH 06/21] x86/insn-eval: Add utility functions to get segment selector Ricardo Neri
2017-04-18 9:42 ` Borislav Petkov
2017-04-26 20:44 ` Ricardo Neri
2017-04-26 20:47 ` Ricardo Neri
2017-04-30 17:15 ` Borislav Petkov
2017-05-05 18:31 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 07/21] x86/insn-eval: Add utility function to get segment descriptor Ricardo Neri
2017-04-19 10:26 ` Borislav Petkov
2017-04-26 21:51 ` Ricardo Neri
2017-05-04 11:02 ` Borislav Petkov
2017-05-12 2:13 ` Ricardo Neri
2017-05-15 17:27 ` Borislav Petkov
2017-03-08 0:32 ` [v6 PATCH 08/21] x86/insn-eval: Add utility function to get segment descriptor base address Ricardo Neri
2017-04-20 8:25 ` Borislav Petkov
2017-04-26 22:37 ` Ricardo Neri
2017-05-05 17:19 ` Borislav Petkov
2017-05-12 2:09 ` Ricardo Neri
2017-04-26 22:52 ` Ricardo Neri
2017-05-05 17:28 ` Borislav Petkov
2017-05-12 2:06 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 09/21] x86/insn-eval: Add functions to get default operand and address sizes Ricardo Neri
2017-04-20 13:06 ` Borislav Petkov
2017-04-27 1:07 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 10/21] x86/insn-eval: Do not use R/EBP as base if mod in ModRM is zero Ricardo Neri
2017-04-21 10:52 ` Borislav Petkov
2017-04-27 1:29 ` Ricardo Neri [this message]
2017-05-07 17:20 ` Borislav Petkov
2017-05-12 1:57 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 11/21] insn/eval: Incorporate segment base in address computation Ricardo Neri
2017-04-21 14:55 ` Borislav Petkov
2017-04-27 1:31 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 12/21] x86/insn: Support both signed 32-bit and 64-bit effective addresses Ricardo Neri
2017-04-25 13:51 ` Borislav Petkov
2017-04-27 3:33 ` Ricardo Neri
2017-05-08 11:42 ` Borislav Petkov
2017-05-12 1:55 ` Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 13/21] x86/insn-eval: Add support to resolve 16-bit addressing encodings Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 14/21] x86/insn-eval: Add wrapper function for 16-bit and 32-bit address encodings Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 15/21] x86/mm: Relocate page fault error codes to traps.h Ricardo Neri
2017-03-08 16:08 ` Andy Lutomirski
2017-03-08 0:32 ` [v6 PATCH 16/21] x86/cpufeature: Add User-Mode Instruction Prevention definitions Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 17/21] x86: Add emulation code for UMIP instructions Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 18/21] x86/umip: Force a page fault when unable to copy emulated result to user Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 19/21] x86/traps: Fixup general protection faults caused by UMIP Ricardo Neri
2017-03-08 15:54 ` Andy Lutomirski
2017-03-08 0:32 ` [v6 PATCH 20/21] x86: Enable User-Mode Instruction Prevention Ricardo Neri
2017-03-08 0:32 ` [v6 PATCH 21/21] selftests/x86: Add tests for " Ricardo Neri
2017-03-08 15:56 ` Andy Lutomirski
2017-03-10 23:38 ` Ricardo Neri
2017-03-08 14:08 ` [v6 PATCH 00/21] x86: Enable " Stas Sergeev
2017-03-08 16:06 ` Andy Lutomirski
2017-03-08 16:29 ` Stas Sergeev
2017-03-08 16:46 ` Andy Lutomirski
2017-03-08 16:53 ` Stas Sergeev
2017-03-09 1:11 ` Ricardo Neri
2017-03-09 22:05 ` Stas Sergeev
2017-03-10 2:41 ` Andy Lutomirski
2017-03-10 10:30 ` Stas Sergeev
2017-03-10 21:04 ` Andy Lutomirski
2017-03-10 21:37 ` Stas Sergeev
2017-03-09 1:15 ` Ricardo Neri
2017-03-09 22:10 ` Stas Sergeev
2017-03-10 2:39 ` Andy Lutomirski
2017-03-10 11:33 ` Stas Sergeev
2017-03-10 14:17 ` Andy Lutomirski
2017-03-11 1:22 ` Ricardo Neri
2017-03-10 23:59 ` Ricardo Neri
2017-03-13 21:25 ` Stas Sergeev
2017-03-27 23:46 ` Ricardo Neri
2017-03-28 9:38 ` Stas Sergeev
2017-03-29 4:38 ` Ricardo Neri
2017-03-29 20:55 ` Stas Sergeev
2017-03-30 5:14 ` Ricardo Neri
2017-03-30 10:10 ` Stas Sergeev
2017-03-31 1:33 ` Ricardo Neri
2017-03-31 14:11 ` Alexandre Julliard
2017-03-31 21:26 ` Stas Sergeev
2017-04-01 2:18 ` Andy Lutomirski
2017-04-04 2:02 ` Ricardo Neri
2017-04-04 6:08 ` Alexandre Julliard
2017-04-01 13:08 ` Stas Sergeev
2017-04-01 17:49 ` H. Peter Anvin
2017-04-02 15:52 ` Andy Lutomirski
2017-04-04 9:59 ` Stas Sergeev
2017-04-04 2:05 ` Ricardo Neri
2017-04-04 8:03 ` Stas Sergeev
2017-03-10 23:58 ` Ricardo Neri
2017-03-09 0:46 ` Ricardo Neri
2017-03-09 22:01 ` Stas Sergeev
2017-03-10 23:47 ` Ricardo Neri
2017-03-10 23:58 ` Stas Sergeev
2017-03-11 0:13 ` Ricardo Neri
2017-03-08 16:07 ` Andy Lutomirski
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