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authorWill Deacon <will.deacon@arm.com>2012-04-27 12:45:07 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-05-07 08:56:37 -0700
commit62a17c9c34a40907e250b5ac110a5c64325f0aef (patch)
parent70403b35a5e2d08c9e2727b2e8dd78cb0b1391b3 (diff)
ARM: 7403/1: tls: remove covert channel via TPIDRURW
commit 6a1c53124aa161eb624ce7b1e40ade728186d34c upstream. TPIDRURW is a user read/write register forming part of the group of thread registers in more recent versions of the ARM architecture (~v6+). Currently, the kernel does not touch this register, which allows tasks to communicate covertly by reading and writing to the register without context-switching affecting its contents. This patch clears TPIDRURW when TPIDRURO is updated via the set_tls macro, which is called directly from __switch_to. Since the current behaviour makes the register useless to userspace as far as thread pointers are concerned, simply clearing the register (rather than saving and restoring it) will not cause any problems to userspace. Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/arm/include/asm/tls.h b/arch/arm/include/asm/tls.h
index 60843eb0f61c..73409e6c0251 100644
--- a/arch/arm/include/asm/tls.h
+++ b/arch/arm/include/asm/tls.h
@@ -7,6 +7,8 @@
.macro set_tls_v6k, tp, tmp1, tmp2
mcr p15, 0, \tp, c13, c0, 3 @ set TLS register
+ mov \tmp1, #0
+ mcr p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register
.macro set_tls_v6, tp, tmp1, tmp2
@@ -15,6 +17,8 @@
mov \tmp2, #0xffff0fff
tst \tmp1, #HWCAP_TLS @ hardware TLS available?
mcrne p15, 0, \tp, c13, c0, 3 @ yes, set TLS register
+ movne \tmp1, #0
+ mcrne p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register
streq \tp, [\tmp2, #-15] @ set TLS value at 0xffff0ff0