kernel.git/arch/mips/kernel/ptrace.c, branch linux-4.15.y

MIPS: Disallow outsized PTRACE_SETREGSET NT_PRFPREG regset accesses

2017-12-12T18:14:12Z

Complement commit c23b3d1a5311 ("MIPS: ptrace: Change GP regset to use correct core dump register layout") and also reject outsized PTRACE_SETREGSET requests to the NT_PRFPREG regset, like with the NT_PRSTATUS regset. Signed-off-by: Maciej W. Rozycki Fixes: c23b3d1a5311 ("MIPS: ptrace: Change GP regset to use correct core dump register layout") Cc: James Hogan Cc: Paul Burton Cc: Alex Smith Cc: Dave Martin Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v3.17+ Patchwork: https://patchwork.linux-mips.org/patch/17930/ Signed-off-by: Ralf Baechle

MIPS: Also verify sizeof `elf_fpreg_t' with PTRACE_SETREGSET

2017-12-12T18:13:42Z

Complement commit d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") and like with the PTRACE_GETREGSET ptrace(2) request also apply a BUILD_BUG_ON check for the size of the `elf_fpreg_t' type in the PTRACE_SETREGSET request handler. Signed-off-by: Maciej W. Rozycki Fixes: d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") Cc: James Hogan Cc: Paul Burton Cc: Alex Smith Cc: Dave Martin Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v4.11+ Patchwork: https://patchwork.linux-mips.org/patch/17929/ Signed-off-by: Ralf Baechle

MIPS: Fix an FCSR access API regression with NT_PRFPREG and MSA

2017-12-12T18:13:12Z

Fix a commit 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset") public API regression, then activated by commit 1db1af84d6df ("MIPS: Basic MSA context switching support"), that caused the FCSR register not to be read or written for CONFIG_CPU_HAS_MSA kernel configurations (regardless of actual presence or absence of the MSA feature in a given processor) with ptrace(2) PTRACE_GETREGSET and PTRACE_SETREGSET requests nor recorded in core dumps. This is because with !CONFIG_CPU_HAS_MSA configurations the whole of `elf_fpregset_t' array is bulk-copied as it is, which includes the FCSR in one half of the last, 33rd slot, whereas with CONFIG_CPU_HAS_MSA configurations array elements are copied individually, and then only the leading 32 FGR slots while the remaining slot is ignored. Correct the code then such that only FGR slots are copied in the respective !MSA and MSA helpers an then the FCSR slot is handled separately in common code. Use `ptrace_setfcr31' to update the FCSR too, so that the read-only mask is respected. Retrieving a correct value of FCSR is important in debugging not only for the human to be able to get the right interpretation of the situation, but for correct operation of GDB as well. This is because the condition code bits in FSCR are used by GDB to determine the location to place a breakpoint at when single-stepping through an FPU branch instruction. If such a breakpoint is placed incorrectly (i.e. with the condition reversed), then it will be missed, likely causing the debuggee to run away from the control of GDB and consequently breaking the process of investigation. Fortunately GDB continues using the older PTRACE_GETFPREGS ptrace(2) request which is unaffected, so the regression only really hits with post-mortem debug sessions using a core dump file, in which case execution, and consequently single-stepping through branches is not possible. Of course core files created by buggy kernels out there will have the value of FCSR recorded clobbered, but such core files cannot be corrected and the person using them simply will have to be aware that the value of FCSR retrieved is not reliable. Which also means we can likely get away without defining a replacement API which would ensure a correct value of FSCR to be retrieved, or none at all. This is based on previous work by Alex Smith, extensively rewritten. Signed-off-by: Alex Smith Signed-off-by: James Hogan Signed-off-by: Maciej W. Rozycki Fixes: 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset") Cc: Paul Burton Cc: Dave Martin Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v3.15+ Patchwork: https://patchwork.linux-mips.org/patch/17928/ Signed-off-by: Ralf Baechle

MIPS: Consistently handle buffer counter with PTRACE_SETREGSET

2017-12-12T18:12:23Z

Update commit d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") bug and consistently consume all data supplied to `fpr_set_msa' with the ptrace(2) PTRACE_SETREGSET request, such that a zero data buffer counter is returned where insufficient data has been given to fill a whole number of FP general registers. In reality this is not going to happen, as the caller is supposed to only supply data covering a whole number of registers and it is verified in `ptrace_regset' and again asserted in `fpr_set', however structuring code such that the presence of trailing partial FP general register data causes `fpr_set_msa' to return with a non-zero data buffer counter makes it appear that this trailing data will be used if there are subsequent writes made to FP registers, which is going to be the case with the FCSR once the missing write to that register has been fixed. Fixes: d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") Signed-off-by: Maciej W. Rozycki Cc: James Hogan Cc: Paul Burton Cc: Alex Smith Cc: Dave Martin Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v4.11+ Patchwork: https://patchwork.linux-mips.org/patch/17927/ Signed-off-by: Ralf Baechle

MIPS: Guard against any partial write attempt with PTRACE_SETREGSET

2017-12-12T18:11:53Z

Complement commit d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") and ensure that no partial register write attempt is made with PTRACE_SETREGSET, as we do not preinitialize any temporaries used to hold incoming register data and consequently random data could be written. It is the responsibility of the caller, such as `ptrace_regset', to arrange for writes to span whole registers only, so here we only assert that it has indeed happened. Signed-off-by: Maciej W. Rozycki Fixes: 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset") Cc: James Hogan Cc: Paul Burton Cc: Alex Smith Cc: Dave Martin Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v3.15+ Patchwork: https://patchwork.linux-mips.org/patch/17926/ Signed-off-by: Ralf Baechle

MIPS: Factor out NT_PRFPREG regset access helpers

2017-12-12T18:11:26Z

In preparation to fix a commit 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset") FCSR access regression factor out NT_PRFPREG regset access helpers for the non-MSA and the MSA variants respectively, to avoid having to deal with excessive indentation in the actual fix. No functional change, however use `target->thread.fpu.fpr[0]' rather than `target->thread.fpu.fpr[i]' for FGR holding type size determination as there's no `i' variable to refer to anymore, and for the factored out `i' variable declaration use `unsigned int' rather than `unsigned' as its type, following the common style. Signed-off-by: Maciej W. Rozycki Fixes: 72b22bbad1e7 ("MIPS: Don't assume 64-bit FP registers for FP regset") Cc: James Hogan Cc: Paul Burton Cc: Alex Smith Cc: Dave Martin Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v3.15+ Patchwork: https://patchwork.linux-mips.org/patch/17925/ Signed-off-by: Ralf Baechle

MIPS/ptrace: Update syscall nr on register changes

2017-11-09T15:13:58Z

Update the thread_info::syscall field when registers are modified via ptrace to change or cancel the system call being entered. This is important to allow seccomp and the syscall entry and exit trace events to observe the new syscall number changed by the normal ptrace hook or seccomp. That includes allowing seccomp's recheck of the system call number after SECCOMP_RET_TRACE to notice if the syscall is changed to a denied one, which happens in seccomp since commit ce6526e8afa4 ("seccomp: recheck the syscall after RET_TRACE") in v4.8. In the process of doing this, the logic to determine whether an indirect system call is in progress (i.e. the O32 ABI's syscall()) is abstracted into mips_syscall_is_indirect(), and a new mips_syscall_update_nr() is used to update the thread_info::syscall based on the register state. The following ptrace operations are updated: - PTRACE_SETREGS (ptrace_setregs()). - PTRACE_SETREGSET with NT_PRSTATUS (gpr32_set() and gpr64_set()). - PTRACE_POKEUSR with 2/v0 or 4/a0 for indirect syscall ([compat_]arch_ptrace()). Fixes: c2d9f1775731 ("MIPS: Fix syscall_get_nr for the syscall exit tracing.") Signed-off-by: James Hogan Cc: Ralf Baechle Cc: Lars Persson Cc: Oleg Nesterov Cc: Kees Cook Cc: Andy Lutomirski Cc: Will Drewry Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/16995/

MIPS/ptrace: Pick up ptrace/seccomp changed syscalls

2017-11-09T15:13:52Z

The MIPS syscall_trace_enter() allows the system call number to be altered or cancelled by a ptrace tracer, via the normal ptrace hook (PTRACE_SYSCALL) and changing the system call number register on entry, and similarly via seccomp (PTRACE_EVENT_SECCOMP when a seccomp filter returns SECCOMP_RET_TRACE). Be sure to update the syscall local variable if this happens, so that seccomp will filter the correct system call number if the normal ptrace hook changes it first, and so that if either the normal ptrace hook or seccomp change it the correct system call number is passed to the trace event. This won't have any effect until the next commit, which fixes ptrace to update thread_info::syscall. Fixes: c2d9f1775731 ("MIPS: Fix syscall_get_nr for the syscall exit tracing.") Signed-off-by: James Hogan Reviewed-by: Kees Cook Cc: Ralf Baechle Cc: Lars Persson Cc: Oleg Nesterov Cc: Kees Cook Cc: Andy Lutomirski Cc: Will Drewry Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/16996/

MIPS: Fix an n32 core file generation regset support regression

2017-11-09T15:04:57Z

Fix a commit 7aeb753b5353 ("MIPS: Implement task_user_regset_view.") regression, then activated by commit 6a9c001b7ec3 ("MIPS: Switch ELF core dumper to use regsets.)", that caused n32 processes to dump o32 core files by failing to set the EF_MIPS_ABI2 flag in the ELF core file header's `e_flags' member: $ file tls-core tls-core: ELF 32-bit MSB executable, MIPS, N32 MIPS64 rel2 version 1 (SYSV), [...] $ ./tls-core Aborted (core dumped) $ file core core: ELF 32-bit MSB core file MIPS, MIPS-I version 1 (SYSV), SVR4-style $ Previously the flag was set as the result of a: statement placed in arch/mips/kernel/binfmt_elfn32.c, however in the regset case, i.e. when CORE_DUMP_USE_REGSET is set, ELF_CORE_EFLAGS is no longer used by `fill_note_info' in fs/binfmt_elf.c, and instead the `->e_flags' member of the regset view chosen is. We have the views defined in arch/mips/kernel/ptrace.c, however only an o32 and an n64 one, and the latter is used for n32 as well. Consequently an o32 core file is incorrectly dumped from n32 processes (the ELF32 vs ELF64 class is chosen elsewhere, and the 32-bit one is correctly selected for n32). Correct the issue then by defining an n32 regset view and using it as appropriate. Issue discovered in GDB testing. Fixes: 7aeb753b5353 ("MIPS: Implement task_user_regset_view.") Signed-off-by: Maciej W. Rozycki Cc: Ralf Baechle Cc: Djordje Todorovic Cc: linux-mips@linux-mips.org Cc: # 3.13+ Patchwork: https://patchwork.linux-mips.org/patch/17617/ Signed-off-by: James Hogan

MIPS: seccomp: Fix indirect syscall args

2017-08-29T13:42:44Z

Since commit 669c4092225f ("MIPS: Give __secure_computing() access to syscall arguments."), upon syscall entry when seccomp is enabled, syscall_trace_enter() passes a carefully prepared struct seccomp_data containing syscall arguments to __secure_computing(). Unfortunately it directly uses mips_get_syscall_arg() and fails to take into account the indirect O32 system calls (i.e. syscall(2)) which put the system call number in a0 and have the arguments shifted up by one entry. We can't just revert that commit as samples/bpf/tracex5 would break again, so use syscall_get_arguments() which already takes indirect syscalls into account instead of directly using mips_get_syscall_arg(), similar to what populate_seccomp_data() does. This also removes the redundant error checking of the mips_get_syscall_arg() return value (get_user() already zeroes the result if an argument from the stack can't be loaded). Reported-by: James Cowgill Fixes: 669c4092225f ("MIPS: Give __secure_computing() access to syscall arguments.") Signed-off-by: James Hogan Reviewed-by: Kees Cook Cc: David Daney Cc: Andy Lutomirski Cc: Will Drewry Cc: Oleg Nesterov Cc: Alexei Starovoitov Cc: Daniel Borkmann Cc: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/16994/ Signed-off-by: Ralf Baechle