linux/arch/arc
Vineet Gupta e4140819da ARC: signal handling robustify
A malicious signal handler / restorer can DOS the system by fudging the
user regs saved on stack, causing weird things such as sigreturn returning
to user mode PC but cpu state still being kernel mode....

Ensure that in sigreturn path status32 always has U bit; any other bogosity
(gargbage PC etc) will be taken care of by normal user mode exceptions mechanisms.

Reproducer signal handler:

    void handle_sig(int signo, siginfo_t *info, void *context)
    {
	ucontext_t *uc = context;
	struct user_regs_struct *regs = &(uc->uc_mcontext.regs);

	regs->scratch.status32 = 0;
    }

Before the fix, kernel would go off to weeds like below:

    --------->8-----------
    [ARCLinux]$ ./signal-test
    Path: /signal-test
    CPU: 0 PID: 61 Comm: signal-test Not tainted 4.0.0-rc5+ #65
    task: 8f177880 ti: 5ffe6000 task.ti: 8f15c000

    [ECR   ]: 0x00220200 => Invalid Write @ 0x00000010 by insn @ 0x00010698
    [EFA   ]: 0x00000010
    [BLINK ]: 0x2007c1ee
    [ERET  ]: 0x10698
    [STAT32]: 0x00000000 :                                   <--------
    BTA: 0x00010680	 SP: 0x5ffe7e48	 FP: 0x00000000
    LPS: 0x20003c6c	LPE: 0x20003c70	LPC: 0x00000000
    ...
    --------->8-----------

Reported-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
2015-03-26 11:19:36 +05:30
..
boot dmaengine: dw: define DW_DMA_MAX_NR_MASTERS 2015-02-04 22:39:44 -08:00
configs ARC: rename default defconfig 2014-12-17 15:23:56 +05:30
include ARC: Fix thread_saved_pc() 2015-02-27 10:59:34 +05:30
kernel ARC: signal handling robustify 2015-03-26 11:19:36 +05:30
lib ARC: switch to generic ENTRY/END assembler annotations 2014-03-26 14:31:28 +05:30
mm ARC: perf: Enable generic software events 2015-02-27 10:15:01 +05:30
oprofile ARC: OProfile support 2013-02-15 23:16:00 +05:30
plat-arcfpga ARC: [arcfpga] Get rid of ARC_BOARD_ANGEL4 and ARC_BOARD_ML509 2014-10-13 14:46:14 +05:30
plat-tb10x ARC: [plat*] move code out of .init_machine into common 2014-10-13 14:46:13 +05:30
Kbuild ARC: Build system: Makefiles, Kconfig, Linker script 2013-02-11 20:00:25 +05:30
Kconfig ARC: add power management options 2014-11-03 18:05:43 +05:30
Kconfig.debug consolidate per-arch stack overflow debugging options 2013-07-04 11:25:39 -07:00
Makefile ARC: rename default defconfig 2014-12-17 15:23:56 +05:30