linux-toradex.git/arch/mips/kernel/signal.c, branch v4.4.26

MIPS: Fix sigreturn via VDSO on microMIPS kernel

2016-06-08T01:14:31+00:00

commit 13eb192d10bcc9ac518d57356179071d603bcb4e upstream.

In microMIPS kernels, handle_signal() sets the isa16 mode bit in the
vdso address so that the sigreturn trampolines (which are offset from
the VDSO) get executed as microMIPS.

However commit ebb5e78cc634 ("MIPS: Initial implementation of a VDSO")
changed the offsets to come from the VDSO image, which already have the
isa16 mode bit set correctly since they're extracted from the VDSO
shared library symbol table.

Drop the isa16 mode bit handling from handle_signal() to fix sigreturn
for cores which support both microMIPS and normal MIPS. This doesn't fix
microMIPS only cores, since the VDSO is still built for normal MIPS, but
thats a separate problem.

Fixes: ebb5e78cc634 ("MIPS: Initial implementation of a VDSO")
Signed-off-by: James Hogan 
Cc: Paul Burton 
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13348/
Signed-off-by: Ralf Baechle 
Signed-off-by: Greg Kroah-Hartman

MIPS: Prevent "restoration" of MSA context in non-MSA kernels

2016-06-08T01:14:31+00:00

commit 6533af4d4831c421cd9aa4dce7cfc19a3514cc09 upstream.

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
Patchwork: https://patchwork.linux-mips.org/patch/13164/
Signed-off-by: Ralf Baechle 
Signed-off-by: Greg Kroah-Hartman

MIPS: Initial implementation of a VDSO

2015-11-11T07:36:36+00:00

Add an initial implementation of a proper (i.e. an ELF shared library)
VDSO. With this commit it does not export any symbols, it only replaces
the current signal return trampoline page. A later commit will add user
implementations of gettimeofday()/clock_gettime().

To support both new toolchains and old ones which don't generate ABI
flags section, we define its content manually and then use a tool
(genvdso) to patch up the section to have the correct name and type.
genvdso also extracts symbol offsets ({,rt_}sigreturn) needed by the
kernel, and generates a C file containing a "struct mips_vdso_image"
containing both the VDSO data and these offsets. This C file is
compiled into the kernel.

On 64-bit kernels we require a different VDSO for each supported ABI,
so we may build up to 3 different VDSOs. The VDSO to use is selected by
the mips_abi structure.

A kernel/user shared data page is created and mapped below the VDSO
image. This is currently empty, but will be used by the user time
function implementations which are added later.

[markos.chandras@imgtec.com:
- Add more comments
- Move abi detection in genvdso.h since it's the get_symbol function
that needs it.
- Add an R6 specific way to calculate the base address of VDSO in order
to avoid the branch instruction which affects performance.
- Do not patch .gnu.attributes since it's not needed for dynamic linking.
- Simplify Makefile a little bit.
- checkpatch fixes
- Restrict VDSO support for binutils < 2.25 for pre-R6
- Include atomic64.h for O32 variant on MIPS64]

Signed-off-by: Alex Smith 
Signed-off-by: Markos Chandras 
Cc: Matthew Fortune 
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11337/
Signed-off-by: Ralf Baechle

MIPS: Add uprobes support.

2015-09-03T10:08:05+00:00

Signed-off-by: Ralf Baechle

MIPS: Save MSA extended context around signals

2015-09-03T10:07:59+00:00

It is desirable for signal handlers to be allowed to make use of MSA,
particularly if auto vectorisation is used when compiling a program.
The MSA context must therefore be saved & restored before & after
invoking the signal handler. Make use of the extended context structs
defined in the preceding patch to save MSA context after the sigframe
when appropriate.

[ralf@linux-mips.org: Fixed conflicts.]

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: Guenter Roeck 
Cc: Matthew Fortune 
Cc: Leonid Yegoshin 
Cc: linux-kernel@vger.kernel.org
Cc: Richard Weinberger 
Cc: James Hogan 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Markos Chandras 
Cc: Manuel Lauss 
Cc: Maciej W. Rozycki 
Patchwork: https://patchwork.linux-mips.org/patch/10796/
Signed-off-by: Ralf Baechle

MIPS: Add definitions for extended context

2015-09-03T10:07:58+00:00

The context introduced by MSA needs to be saved around signals. However,
we can't increase the size of struct sigcontext because that will change
the offset of the signal mask in struct sigframe or struct ucontext.
This patch instead places the new context immediately after the struct
sigframe for traditional signals, or similarly after struct ucontext for
RT signals. The layout of struct sigframe & struct ucontext is identical
from their sigcontext fields onwards, so the offset from the sigcontext
to the extended context will always be the same regardless of the type
of signal.

Userland will be able to search through the extended context by using
the magic values to detect which types of context are present. Any
unrecognised context can be skipped over using the size field of struct
extcontext. Once the magic value END_EXTCONTEXT_MAGIC is seen it is
known that there are no further extended context structures to examine.

This approach is somewhat similar to that taken by ARM to save VFP &
other context at the end of struct ucontext.

Userland can determine whether extended context is present by checking
for the USED_EXTCONTEXT bit in the sc_used_math field of struct
sigcontext. Whilst this could potentially change the historic semantics
of sc_used_math if further extended context which does not imply FP
context were to be introduced in the future, I have been unable to find
any userland code making use of sc_used_math at all. Using one of the
fields described as unused in struct sigcontext was considered, but the
kernel does not already write to those fields so there would be no
guarantee of the field being clear on older kernels. Other alternatives
would be to have userland check the kernel version, or to have a HWCAP
bit indicating presence of extended context. However there is a desire
to have the context & information required to decode it be self
contained such that, for example, debuggers could decode the saved
context easily.

[ralf@linux-mips.org: Fixed conflict.]

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: Guenter Roeck 
Cc: Matthew Fortune 
Cc: Peter Zijlstra 
Cc: Zubair Lutfullah Kakakhel 
Cc: Alex Smith 
Cc: linux-kernel@vger.kernel.org
Cc: Richard Weinberger 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Michael Ellerman 
Cc: Markos Chandras 
Cc: Daniel Borkmann 
Cc: Maciej W. Rozycki 
Patchwork: https://patchwork.linux-mips.org/patch/10795/
Signed-off-by: Ralf Baechle

MIPS: Indicate FP mode in sigcontext sc_used_math

2015-09-03T10:07:56+00:00

The sc_used_math field of struct sigcontext & its variants has
traditionally been used as a boolean value indicating only whether or
not floating point context is saved within the sigcontext. With various
supported FP modes & the ability to switch between them this information
will no longer be enough to decode the meaning of the data stored in the
sc_fpregs fields of struct sigcontext.

To make that possible 3 bits are defined within sc_used_math:

  - Bit 0 (USED_FP) represents whether FP was used, essentially
    providing the boolean flag which sc_used_math as a whole provided
    previously.

  - Bit 1 (USED_FR1) provides the value of the Status.FR bit at the time
    the FP context was saved.

  - Bit 2 (USED_HYBRID_FPRS) indicates whether the FP context was saved
    under the hybrid FPR scheme. Essentially, when set the odd singles
    are located in bits 63:32 of the preceding even indexed sc_fpregs
    element.

Any userland that tests whether the sc_used_math field is zero or
non-zero will continue to function as expected. Having said that, I
could not find any userland which uses the sc_used_math field at all.

[ralf@linux-mips.org: Fixed rejects.]

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: Guenter Roeck 
Cc: Matthew Fortune 
Cc: Michael Ellerman 
Cc: linux-kernel@vger.kernel.org
Cc: Richard Weinberger 
Cc: Andy Lutomirski 
Cc: Maciej W. Rozycki 
Patchwork: https://patchwork.linux-mips.org/patch/10794/
Signed-off-by: Ralf Baechle

MIPS: Use common FP sigcontext code for O32 compat

2015-09-03T10:07:56+00:00

Make use of the common FP sigcontext code for O32 binaries running on
MIPS64 kernels now that it is taking appropriate offsets into struct
sigcontext(32) from struct mips_abi.

[ralf@linux-mips.org: Fixed reject.]

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: Guenter Roeck 
Cc: Matthew Fortune 
Cc: Leonid Yegoshin 
Cc: Michael Ellerman 
Cc: linux-kernel@vger.kernel.org
Cc: Richard Weinberger 
Cc: James Hogan 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Markos Chandras 
Cc: Manuel Lauss 
Cc: Maciej W. Rozycki 
Patchwork: https://patchwork.linux-mips.org/patch/10792/
Signed-off-by: Ralf Baechle

MIPS: Skip odd double FP registers when copying FP32 sigcontext

2015-09-03T10:07:56+00:00

When a task uses 32 bit floating point, the odd indexed 32b register
values are stored in bits 63:32 of the preceding even indexed 64b
FP register field in saved context. Thus there is no point in
preserving the odd indexed 64b register fields since they hold no
valid context. This patch will cause them to be skipped, as is
already done in arch/mips/kernel/signal32.c.

[ralf@linux-mips.org: Fixed reject.]

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: Guenter Roeck 
Cc: Matthew Fortune 
Cc: Michael Ellerman 
Cc: linux-kernel@vger.kernel.org
Cc: Richard Weinberger 
Cc: Andy Lutomirski 
Cc: Maciej W. Rozycki 
Cc: Andrew Morton 
Patchwork: https://patchwork.linux-mips.org/patch/10791/
Signed-off-by: Ralf Baechle

MIPS: Move FP usage checks into protected_{save, restore}_fp_context

2015-09-03T10:07:55+00:00

In preparation for sharing protected_{save,restore}_fp_context with
compat ABIs, move the FP usage checks into said functions. This will
both enable that code to be shared, and allow for extensions of it in
further patches to also be shared.

Signed-off-by: Paul Burton 
Cc: linux-mips@linux-mips.org
Cc: Guenter Roeck 
Cc: Matthew Fortune 
Cc: Michael Ellerman 
Cc: linux-kernel@vger.kernel.org
Cc: Richard Weinberger 
Cc: Andy Lutomirski 
Cc: Maciej W. Rozycki 
Patchwork: https://patchwork.linux-mips.org/patch/10790/
Signed-off-by: Ralf Baechle