ARM: 8687/1: signal: Fix unparseable iwmmxt_sigframe in uc_regspace[]
In kernels with CONFIG_IWMMXT=y running on non-iWMMXt hardware, the
signal frame can be left partially uninitialised in such a way
that userspace cannot parse uc_regspace[] safely. In particular,
this means that the VFP registers cannot be located reliably in the
signal frame when a multi_v7_defconfig kernel is run on the
majority of platforms.
The cause is that the uc_regspace[] is laid out statically based on
the kernel config, but the decision of whether to save/restore the
iWMMXt registers must be a runtime decision.
To minimise breakage of software that may assume a fixed layout,
this patch emits a dummy block of the same size as iwmmxt_sigframe,
for non-iWMMXt threads. However, the magic and size of this block
are now filled in to help parsers skip over it. A new DUMMY_MAGIC
is defined for this purpose.
It is probably legitimate (if non-portable) for userspace to
manufacture its own sigframe for sigreturn, and there is no obvious
reason why userspace should be required to insert a DUMMY_MAGIC
block when running on non-iWMMXt hardware, when omitting it has
worked just fine forever in other configurations. So in this case,
sigreturn does not require this block to be present.
Reported-by: Edmund Grimley-Evans <Edmund.Grimley-Evans@arm.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
diff --git a/arch/arm/include/asm/ucontext.h b/arch/arm/include/asm/ucontext.h
index 14749ae..921d827 100644
--- a/arch/arm/include/asm/ucontext.h
+++ b/arch/arm/include/asm/ucontext.h
@@ -35,6 +35,12 @@ struct ucontext {
* bytes, to prevent unpredictable padding in the signal frame.
*/
+/*
+ * Dummy padding block: if this magic is encountered, the block should
+ * be skipped using the corresponding size field.
+ */
+#define DUMMY_MAGIC 0xb0d9ed01
+
#ifdef CONFIG_CRUNCH
#define CRUNCH_MAGIC 0x5065cf03
#define CRUNCH_STORAGE_SIZE (CRUNCH_SIZE + 8)