If a kernel doesn't support MSA context (ie. CONFIG_CPU_HAS_MSA=n) then it will only keep 64 bits per FP register in thread context, and the calls to set_fpr64 in restore_msa_extcontext will overrun the end of the FP register context into the FCSR & MSACSR values. GCC 6.x has become smart enough to detect this & complain like so: arch/mips/kernel/signal.c: In function 'protected_restore_fp_context': ./arch/mips/include/asm/processor.h:114:17: error: array subscript is above array bounds [-Werror=array-bounds] fpr->val##width[FPR_IDX(width, idx)] = val; \ ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ ./arch/mips/include/asm/processor.h:118:1: note: in expansion of macro 'BUILD_FPR_ACCESS' BUILD_FPR_ACCESS(64) The only way to trigger this code to run would be for a program to set up an artificial extended MSA context structure following a sigframe & execute sigreturn. Whilst this doesn't allow a program to write to any state that it couldn't already, it makes little sense to allow this "restoration" of MSA context in a system that doesn't support MSA. Fix this by killing a program with SIGSYS if it tries something as crazy as "restoring" fake MSA context in this way, also fixing the build error & allowing for most of restore_msa_extcontext to be optimised out of kernels without support for MSA. Signed-off-by: Paul Burton <paul.burton@xxxxxxxxxx> Reported-by: Michal Toman <michal.toman@xxxxxxxxxx> Fixes: bf82cb30c7e5 ("MIPS: Save MSA extended context around signals") Cc: James Hogan <james.hogan@xxxxxxxxxx> Cc: stable <stable@xxxxxxxxxxxxxxx> # v4.3+ --- arch/mips/kernel/signal.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c index bf792e2..a304b70 100644 --- a/arch/mips/kernel/signal.c +++ b/arch/mips/kernel/signal.c @@ -195,6 +195,9 @@ static int restore_msa_extcontext(void __user *buf, unsigned int size) unsigned int csr; int i, err; + if (!config_enabled(CONFIG_CPU_HAS_MSA)) + return SIGSYS; + if (size != sizeof(*msa)) return -EINVAL; -- 2.8.0 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html