linux-kernel - [PATCH] x86: Make sure get_user

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:	Wed,  4 Nov 2009 15:11:33 +0100
From:	Chris Lalancette <clalance@...hat.com>
To:	mingo@...e.hu
Cc:	x86@...nel.org, mingo@...hat.com, kvm@...r.kernel.org,
	pbonzini@...hat.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, hpa@...or.com,
	Chris Lalancette <clalance@...hat.com>
Subject: [PATCH] x86: Make sure get_user_desc() doesn't sign extend.

The current implementation of get_user_desc() sign extends
the return value because of integer promotion rules.  For
the most part, this doesn't matter, because the top bit of
base2 is usually 0.  If, however, that bit is 1, then the
entire value will be 0xffff... which is probably not what
the caller intended.  This patch casts the entire thing
to unsigned before returning, which generates almost the
same assembly as the current code but replaces the final
"cltq" (sign extend) with a "mov %eax %eax" (zero-extend).
This fixes booting certain guests under KVM.

(3rd retry, no response to the previous 2)

Signed-off-by: Chris Lalancette <clalance@...hat.com>
---
 arch/x86/include/asm/desc.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index e8de2f6..617bd56 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -288,7 +288,7 @@ static inline void load_LDT(mm_context_t *pc)
 
 static inline unsigned long get_desc_base(const struct desc_struct *desc)
 {
-	return desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24);
+	return (unsigned)(desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24));
 }
 
 static inline void set_desc_base(struct desc_struct *desc, unsigned long base)
-- 
1.6.0.6

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/