From ce184a0dee92a0a333236a26478e304dca29a3df Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Fri, 30 Jun 2017 18:56:59 +0100 Subject: 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 Signed-off-by: Dave Martin Signed-off-by: Russell King --- arch/arm/include/asm/ucontext.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'arch/arm/include/asm') diff --git a/arch/arm/include/asm/ucontext.h b/arch/arm/include/asm/ucontext.h index 14749aec94bf..921d8274855c 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) -- cgit