[2.6.22.y] {03/14} - Handle bogus %cs selector in single-step instruction decoding - on top of 2.6.22.17

[Oliver Pinter]

aka: handle-bogus-%cs-selector-in-single-step-instruction-decoding.patch

From: Roland McGrath <roland@xxxxxxxxxx>
Date: Mon, 16 Jul 2007 08:03:16 +0000 (-0700)
Subject: Handle bogus %cs selector in single-step instruction decoding
Patch-mainline: 2.6.23-rc1
References: 326270, CVE-2007-3731

Handle bogus %cs selector in single-step instruction decoding

mainline: 29eb51101c02df517ca64ec472d7501127ad1da8

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@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Jeff Mahoney <jeffm@xxxxxxxx>
CC: Oliver Pinter <oliver.pntr@xxxxxxxxx>
---

 arch/i386/kernel/ptrace.c   |   22 +++++++++++++++-------
 arch/x86_64/kernel/ptrace.c |   23 ++++++++++++++++-------
 2 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
index 1c075f5..0c8f00e 100644
--- a/arch/i386/kernel/ptrace.c
+++ b/arch/i386/kernel/ptrace.c
@@ -164,14 +164,22 @@ static unsigned long
convert_eip_to_linear(struct task_struct *child, struct pt_
 		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 --git a/arch/x86_64/kernel/ptrace.c b/arch/x86_64/kernel/ptrace.c
index fa6775e..e83cc67 100644
--- a/arch/x86_64/kernel/ptrace.c
+++ b/arch/x86_64/kernel/ptrace.c
@@ -102,16 +102,25 @@ unsigned long convert_rip_to_linear(struct
task_struct *child, struct pt_regs *r
 		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;
 }



-- 
Thanks,
Oliver
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