From: Roland McGrath <roland@redhat.com>
Date: Mon, 16 Jul 2007 08:03:16 +0000 (-0700)
Subject: Handle bogus %cs selector in single-step instruction decoding
X-Git-Tag: v2.6.23-rc1~492
X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=29eb51101c02df517ca64ec472d7501127ad1da8

Handle bogus %cs selector in single-step instruction decoding

The code for LDT segment selectors was not robust in the face of a bogus
selector set in %cs via ptrace before the single-step was done.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

Adjusted to apply to Debian's 2.6.18 by dann frazier <dannf@debian.org>

diff -urpN linux-source-2.6.18.orig/arch/i386/kernel/ptrace.c linux-source-2.6.18/arch/i386/kernel/ptrace.c
--- linux-source-2.6.18.orig/arch/i386/kernel/ptrace.c	2006-09-19 21:42:06.000000000 -0600
+++ linux-source-2.6.18/arch/i386/kernel/ptrace.c	2007-09-19 23:45:45.949576125 -0600
@@ -172,14 +172,22 @@ static unsigned long convert_eip_to_line
 		u32 *desc;
 		unsigned long base;
 
-		down(&child->mm->context.sem);
-		desc = child->mm->context.ldt + (seg & ~7);
-		base = (desc[0] >> 16) | ((desc[1] & 0xff) << 16) | (desc[1] & 0xff000000);
+		seg &= ~7UL;
 
-		/* 16-bit code segment? */
-		if (!((desc[1] >> 22) & 1))
-			addr &= 0xffff;
-		addr += base;
+		down(&child->mm->context.sem);
+		if (unlikely((seg >> 3) >= child->mm->context.size))
+			addr = -1L; /* bogus selector, access would fault */
+		else {
+			desc = child->mm->context.ldt + seg;
+			base = ((desc[0] >> 16) |
+				((desc[1] & 0xff) << 16) |
+				(desc[1] & 0xff000000));
+
+			/* 16-bit code segment? */
+			if (!((desc[1] >> 22) & 1))
+				addr &= 0xffff;
+			addr += base;
+		}
 		up(&child->mm->context.sem);
 	}
 	return addr;
diff -urpN linux-source-2.6.18.orig/arch/x86_64/kernel/ptrace.c linux-source-2.6.18/arch/x86_64/kernel/ptrace.c
--- linux-source-2.6.18.orig/arch/x86_64/kernel/ptrace.c	2006-09-19 21:42:06.000000000 -0600
+++ linux-source-2.6.18/arch/x86_64/kernel/ptrace.c	2007-09-19 23:45:45.953575027 -0600
@@ -103,16 +103,25 @@ unsigned long convert_rip_to_linear(stru
 		u32 *desc;
 		unsigned long base;
 
-		down(&child->mm->context.sem);
-		desc = child->mm->context.ldt + (seg & ~7);
-		base = (desc[0] >> 16) | ((desc[1] & 0xff) << 16) | (desc[1] & 0xff000000);
+		seg &= ~7UL;
 
-		/* 16-bit code segment? */
-		if (!((desc[1] >> 22) & 1))
-			addr &= 0xffff;
-		addr += base;
+		down(&child->mm->context.sem);
+		if (unlikely((seg >> 3) >= child->mm->context.size))
+			addr = -1L; /* bogus selector, access would fault */
+		else {
+			desc = child->mm->context.ldt + seg;
+			base = ((desc[0] >> 16) |
+				((desc[1] & 0xff) << 16) |
+				(desc[1] & 0xff000000));
+
+			/* 16-bit code segment? */
+			if (!((desc[1] >> 22) & 1))
+				addr &= 0xffff;
+			addr += base;
+		}
 		up(&child->mm->context.sem);
 	}
+
 	return addr;
 }