• Steven Rostedt's avatar
    ftrace, x86: make kernel text writable only for conversions · 16239630
    Steven Rostedt authored
    Impact: keep kernel text read only
    
    Because dynamic ftrace converts the calls to mcount into and out of
    nops at run time, we needed to always keep the kernel text writable.
    
    But this defeats the point of CONFIG_DEBUG_RODATA. This patch converts
    the kernel code to writable before ftrace modifies the text, and converts
    it back to read only afterward.
    
    The kernel text is converted to read/write, stop_machine is called to
    modify the code, then the kernel text is converted back to read only.
    
    The original version used SYSTEM_STATE to determine when it was OK
    or not to change the code to rw or ro. Andrew Morton pointed out that
    using SYSTEM_STATE is a bad idea since there is no guarantee to what
    its state will actually be.
    
    Instead, I moved the check into the set_kernel_text_* functions
    themselves, and use a local variable to determine when it is
    OK to change the kernel text RW permissions.
    
    [ Update: Ingo Molnar suggested moving the prototypes to cacheflush.h ]
    Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
    16239630
ftrace.c 12.8 KB