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: [PATCH v7 12/26] x86/insn-eval: Add utility functions to get segment descriptor base address and limit
Date: Sat, 03 Jun 2017 10:23:12 -0700 [thread overview]
Message-ID: <1496510592.24288.67.camel@ranerica-desktop> (raw)
In-Reply-To: <20170531165839.6nlkmdlrqnuloulz@pd.tnic>
On Wed, 2017-05-31 at 18:58 +0200, Borislav Petkov wrote:
> On Fri, May 05, 2017 at 11:17:10AM -0700, Ricardo Neri wrote:
> > With segmentation, the base address of the segment descriptor is needed
> > to compute a linear address. The segment descriptor used in the address
> > computation depends on either any segment override prefixes in the
> > instruction or the default segment determined by the registers involved
> > in the address computation. Thus, both the instruction as well as the
> > register (specified as the offset from the base of pt_regs) are given as
> > inputs, along with a boolean variable to select between override and
> > default.
>
> ...
>
> > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
> > index f46cb31..c77ed80 100644
> > --- a/arch/x86/lib/insn-eval.c
> > +++ b/arch/x86/lib/insn-eval.c
> > @@ -476,6 +476,133 @@ static struct desc_struct *get_desc(unsigned short sel)
> > }
> >
> > /**
> > + * insn_get_seg_base() - Obtain base address of segment descriptor.
> > + * @regs: Structure with register values as seen when entering kernel mode
> > + * @insn: Instruction structure with selector override prefixes
> > + * @regoff: Operand offset, in pt_regs, of which the selector is needed
> > + *
> > + * Obtain the base address of the segment descriptor as indicated by either
> > + * any segment override prefixes contained in insn or the default segment
> > + * applicable to the register indicated by regoff. regoff is specified as the
> > + * offset in bytes from the base of pt_regs.
> > + *
> > + * Return: In protected mode, base address of the segment. Zero in for long
> > + * mode, except when FS or GS are used. In virtual-8086 mode, the segment
> > + * selector shifted 4 positions to the right. -1L in case of
> > + * error.
> > + */
> > +unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn,
> > + int regoff)
> > +{
> > + struct desc_struct *desc;
> > + unsigned short sel;
> > + enum segment_register seg_reg;
> > +
> > + seg_reg = resolve_seg_register(insn, regs, regoff);
> > + if (seg_reg == SEG_REG_INVAL)
> > + return -1L;
> > +
> > + sel = get_segment_selector(regs, seg_reg);
> > + if ((short)sel < 0)
>
> I guess it would be better if that function returned a signed short so
> you don't have to cast it here. (You're casting it to an unsigned long
> below anyway.)
Yes, this make sense. I will make this change.
>
> > + return -1L;
> > +
> > + if (v8086_mode(regs))
> > + /*
> > + * Base is simply the segment selector shifted 4
> > + * positions to the right.
> > + */
> > + return (unsigned long)(sel << 4);
> > +
>
> ...
>
> > +static unsigned long get_seg_limit(struct pt_regs *regs, struct insn *insn,
> > + int regoff)
> > +{
> > + struct desc_struct *desc;
> > + unsigned short sel;
> > + unsigned long limit;
> > + enum segment_register seg_reg;
> > +
> > + seg_reg = resolve_seg_register(insn, regs, regoff);
> > + if (seg_reg == SEG_REG_INVAL)
> > + return 0;
> > +
> > + sel = get_segment_selector(regs, seg_reg);
> > + if ((short)sel < 0)
>
> Ditto.
Here as well.
>
> > + return 0;
> > +
> > + if (user_64bit_mode(regs) || v8086_mode(regs))
> > + return -1L;
> > +
> > + if (!sel)
> > + return 0;
> > +
> > + desc = get_desc(sel);
> > + if (!desc)
> > + return 0;
> > +
> > + /*
> > + * If the granularity bit is set, the limit is given in multiples
> > + * of 4096. When the granularity bit is set, the least 12 significant
>
> the 12 least significant bits
>
> > + * bits are not tested when checking the segment limits. In practice,
> > + * this means that the segment ends in (limit << 12) + 0xfff.
> > + */
> > + limit = get_desc_limit(desc);
> > + if (desc->g)
> > + limit <<= 12 | 0x7;
>
> That 0x7 doesn't look like 0xfff - it shifts limit by 15 instead. You
> can simply write it like you mean it:
>
> limit = (limit << 12) + 0xfff;
You are right, this wrong. I will implement as you mention.
Thanks and BR,
Ricardo
next prev parent reply other threads:[~2017-06-03 17:23 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-05 18:16 [PATCH v7 00/26] x86: Enable User-Mode Instruction Prevention Ricardo Neri
2017-05-05 18:16 ` [PATCH v7 01/26] ptrace,x86: Make user_64bit_mode() available to 32-bit builds Ricardo Neri
2017-05-21 14:19 ` Borislav Petkov
2017-05-05 18:17 ` [PATCH v7 02/26] x86/mm: Relocate page fault error codes to traps.h Ricardo Neri
2017-05-21 14:23 ` Borislav Petkov
2017-05-27 3:40 ` Ricardo Neri
2017-05-27 10:13 ` Borislav Petkov
2017-06-01 3:09 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 03/26] x86/mpx: Use signed variables to compute effective addresses Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 04/26] x86/mpx: Do not use SIB.index if its value is 100b and ModRM.mod is not 11b Ricardo Neri
2017-05-24 13:37 ` Borislav Petkov
2017-05-27 3:36 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 05/26] x86/mpx: Do not use SIB.base if its value is 101b and ModRM.mod = 0 Ricardo Neri
2017-05-29 13:07 ` Borislav Petkov
2017-06-06 6:08 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 06/26] x86/mpx, x86/insn: Relocate insn util functions to a new insn-eval file Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 07/26] x86/insn-eval: Do not BUG on invalid register type Ricardo Neri
2017-05-29 16:37 ` Borislav Petkov
2017-06-06 6:06 ` Ricardo Neri
2017-06-06 11:58 ` Borislav Petkov
2017-06-07 0:28 ` Ricardo Neri
2017-06-07 12:21 ` Borislav Petkov
2017-05-05 18:17 ` [PATCH v7 08/26] x86/insn-eval: Add a utility function to get register offsets Ricardo Neri
2017-05-29 17:16 ` Borislav Petkov
2017-06-06 6:02 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 09/26] x86/insn-eval: Add utility function to identify string instructions Ricardo Neri
2017-05-29 21:48 ` Borislav Petkov
2017-06-06 6:01 ` Ricardo Neri
2017-06-06 12:04 ` Borislav Petkov
2017-05-05 18:17 ` [PATCH v7 10/26] x86/insn-eval: Add utility functions to get segment selector Ricardo Neri
2017-05-30 10:35 ` Borislav Petkov
2017-06-15 18:37 ` Ricardo Neri
2017-06-15 19:04 ` Ricardo Neri
2017-06-19 15:29 ` Borislav Petkov
2017-06-19 15:37 ` Borislav Petkov
2017-05-05 18:17 ` [PATCH v7 11/26] x86/insn-eval: Add utility function to get segment descriptor Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 12/26] x86/insn-eval: Add utility functions to get segment descriptor base address and limit Ricardo Neri
2017-05-31 16:58 ` Borislav Petkov
2017-06-03 17:23 ` Ricardo Neri [this message]
2017-05-05 18:17 ` [PATCH v7 13/26] x86/insn-eval: Add function to get default params of code segment Ricardo Neri
2017-06-07 12:59 ` Borislav Petkov
2017-06-15 19:24 ` Ricardo Neri
2017-06-19 17:11 ` Borislav Petkov
2017-05-05 18:17 ` [PATCH v7 14/26] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 5 Ricardo Neri
2017-06-07 13:15 ` Borislav Petkov
2017-06-15 19:36 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 15/26] x86/insn-eval: Incorporate segment base and limit in linear address computation Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 16/26] x86/insn-eval: Support both signed 32-bit and 64-bit effective addresses Ricardo Neri
2017-06-07 15:48 ` Borislav Petkov
2017-07-25 23:48 ` Ricardo Neri
2017-07-27 13:26 ` Borislav Petkov
2017-07-28 2:04 ` Ricardo Neri
2017-07-28 6:50 ` Borislav Petkov
2017-06-07 15:49 ` Borislav Petkov
2017-06-15 19:58 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 17/26] x86/insn-eval: Handle 32-bit address encodings in virtual-8086 mode Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 18/26] x86/insn-eval: Add support to resolve 16-bit addressing encodings Ricardo Neri
2017-06-07 16:28 ` Borislav Petkov
2017-06-15 21:50 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 19/26] x86/insn-eval: Add wrapper function for 16-bit and 32-bit address encodings Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 20/26] x86/cpufeature: Add User-Mode Instruction Prevention definitions Ricardo Neri
2017-05-06 9:04 ` Paolo Bonzini
2017-05-11 3:23 ` Ricardo Neri
2017-06-07 18:24 ` Borislav Petkov
2017-05-05 18:17 ` [PATCH v7 21/26] x86: Add emulation code for UMIP instructions Ricardo Neri
2017-06-08 18:38 ` Borislav Petkov
2017-06-17 1:34 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 22/26] x86/umip: Force a page fault when unable to copy emulated result to user Ricardo Neri
2017-06-09 11:02 ` Borislav Petkov
2017-07-25 23:50 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 23/26] x86/traps: Fixup general protection faults caused by UMIP Ricardo Neri
2017-06-09 13:02 ` Borislav Petkov
2017-07-25 23:51 ` Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 24/26] x86: Enable User-Mode Instruction Prevention Ricardo Neri
2017-06-09 16:10 ` Borislav Petkov
2017-07-26 0:44 ` Ricardo Neri
2017-07-27 13:57 ` Borislav Petkov
2017-05-05 18:17 ` [PATCH v7 25/26] selftests/x86: Add tests for " Ricardo Neri
2017-05-05 18:17 ` [PATCH v7 26/26] selftests/x86: Add tests for instruction str and sldt Ricardo Neri
2017-05-17 18:42 ` [PATCH v7 00/26] x86: Enable User-Mode Instruction Prevention Ricardo Neri
2017-05-27 3:49 ` Neri, Ricardo
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