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author | Paul Burton <paul.burton@imgtec.com> | 2016-04-21 18:04:53 +0100 |
---|---|---|
committer | Ralf Baechle <ralf@linux-mips.org> | 2016-05-13 15:35:57 +0200 |
commit | 6533af4d4831c421cd9aa4dce7cfc19a3514cc09 (patch) | |
tree | 9e607fd7cadb6a1a95c97480726ea3e47e07b23d /arch | |
parent | 1fa405552e33f2169d173cdb7ca0c03e094904f6 (diff) | |
download | linux-6533af4d4831c421cd9aa4dce7cfc19a3514cc09.tar.bz2 |
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 <paul.burton@imgtec.com>
Reported-by: Michal Toman <michal.toman@imgtec.com>
Fixes: bf82cb30c7e5 ("MIPS: Save MSA extended context around signals")
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Michal Toman <michal.toman@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: stable <stable@vger.kernel.org> # v4.3+
Patchwork: https://patchwork.linux-mips.org/patch/13164/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/mips/kernel/signal.c | 7 |
1 files 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; } |