From 6533af4d4831c421cd9aa4dce7cfc19a3514cc09 Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Thu, 21 Apr 2016 18:04:53 +0100 Subject: [PATCH] MIPS: Prevent "restoration" of MSA context in non-MSA kernels 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 Reported-by: Michal Toman Fixes: bf82cb30c7e5 ("MIPS: Save MSA extended context around signals") Tested-by: Aaro Koskinen Cc: James Hogan Cc: Michal Toman Cc: linux-mips@linux-mips.org Cc: stable # v4.3+ Patchwork: https://patchwork.linux-mips.org/patch/13164/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/signal.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c index 5f18d0b879e0..ab042291fbfd 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; @@ -398,8 +401,8 @@ int protected_restore_fp_context(void __user *sc) } fp_done: - if (used & USED_EXTCONTEXT) - err |= restore_extcontext(sc_to_extcontext(sc)); + if (!err && (used & USED_EXTCONTEXT)) + err = restore_extcontext(sc_to_extcontext(sc)); return err ?: sig; }