linux-kernel - [PATCH v10 01/13] x86/insn-eval: Extend get_seg_base

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Date:   Fri, 27 Oct 2017 16:51:38 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, ricardo.neri@...el.com,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Adam Buchbinder <adam.buchbinder@...il.com>,
        Colin Ian King <colin.king@...onical.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Qiaowei Ren <qiaowei.ren@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: [PATCH v10 01/13] x86/insn-eval: Extend get_seg_base_addr() to also obtain segment limit

In protected mode, it is common to want to obtain the limit of a segment
along with its base address. This is useful, for instance, to verify that
an effective address lies within a segment before computing a linear
address.

Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Adam Buchbinder <adam.buchbinder@...il.com>
Cc: Colin Ian King <colin.king@...onical.com>
Cc: Lorenzo Stoakes <lstoakes@...il.com>
Cc: Qiaowei Ren <qiaowei.ren@...el.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Thomas Garnier <thgarnie@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
Cc: x86@...nel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Up to this point, this library only computes linear addresses in long
mode. Subsequent patches will include support for protected mode. Support
to verify the segment limit will be needed.
---
 arch/x86/lib/insn-eval.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 1c23ec0..91f08aa 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -729,25 +729,29 @@ int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs)
 }
 
 /**
- * get_seg_base_addr() - obtain base address of a segment
+ * get_seg_base_limit() - obtain base address and limit of a segment
  * @insn:	Instruction. Must be valid.
  * @regs:	Register values as seen when entering kernel mode
  * @regoff:	Operand offset, in pt_regs, used to resolve segment descriptor
  * @base:	Obtained segment base
+ * @limit:	Obtained segment limit
  *
- * Obtain the base address of the segment associated with the operand @regoff
- * and, if any or allowed, override prefixes in @insn. This function is
+ * Obtain the base address and limit of the segment associated with the operand
+ * @regoff and, if any or allowed, override prefixes in @insn. This function is
  * different from insn_get_seg_base() as the latter does not resolve the segment
- * associated with the instruction operand.
+ * associated with the instruction operand. If a limit is not needed (e.g.,
+ * when running in long mode), @limit can be NULL.
  *
  * Returns:
  *
- * 0 on success. @base will contain the base address of the resolved segment.
+ * 0 on success. @base and @limit will contain the base address and of the
+ * resolved segment, respectively.
  *
  * -EINVAL on error.
  */
-static int get_seg_base_addr(struct insn *insn, struct pt_regs *regs,
-			     int regoff, unsigned long *base)
+static int get_seg_base_limit(struct insn *insn, struct pt_regs *regs,
+			      int regoff, unsigned long *base,
+			      unsigned long *limit)
 {
 	int seg_reg_idx;
 
@@ -762,6 +766,13 @@ static int get_seg_base_addr(struct insn *insn, struct pt_regs *regs,
 	if (*base == -1L)
 		return -EINVAL;
 
+	if (!limit)
+		return 0;
+
+	*limit = get_seg_limit(regs, seg_reg_idx);
+	if (!(*limit))
+		return -EINVAL;
+
 	return 0;
 }
 
@@ -843,7 +854,7 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 		eff_addr += insn->displacement.value;
 	}
 
-	ret = get_seg_base_addr(insn, regs, addr_offset, &seg_base);
+	ret = get_seg_base_limit(insn, regs, addr_offset, &seg_base, NULL);
 	if (ret)
 		goto out;
 
-- 
2.7.4