• Dave Hansen's avatar
    x86/pkeys: Properly copy pkey state at fork() · a31e184e
    Dave Hansen authored
    Memory protection key behavior should be the same in a child as it was
    in the parent before a fork.  But, there is a bug that resets the
    state in the child at fork instead of preserving it.
    
    The creation of new mm's is a bit convoluted.  At fork(), the code
    does:
    
      1. memcpy() the parent mm to initialize child
      2. mm_init() to initalize some select stuff stuff
      3. dup_mmap() to create true copies that memcpy() did not do right
    
    For pkeys two bits of state need to be preserved across a fork:
    'execute_only_pkey' and 'pkey_allocation_map'.
    
    Those are preserved by the memcpy(), but mm_init() invokes
    init_new_context() which overwrites 'execute_only_pkey' and
    'pkey_allocation_map' with "new" values.
    
    The author of the code erroneously believed that init_new_context is *only*
    called at execve()-time.  But, alas, init_new_context() is used at execve()
    and fork().
    
    The result is that, after a fork(), the child's pkey state ends up looking
    like it does after an execve(), which is totally wrong.  pkeys that are
    already allocated can be allocated again, for instance.
    
    To fix this, add code called by dup_mmap() to copy the pkey state from
    parent to child explicitly.  Also add a comment above init_new_context() to
    make it more clear to the next poor sod what this code is used for.
    
    Fixes: e8c24d3a ("x86/pkeys: Allocation/free syscalls")
    Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Cc: bp@alien8.de
    Cc: hpa@zytor.com
    Cc: peterz@infradead.org
    Cc: mpe@ellerman.id.au
    Cc: will.deacon@arm.com
    Cc: luto@kernel.org
    Cc: jroedel@suse.de
    Cc: stable@vger.kernel.org
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Michael Ellerman <mpe@ellerman.id.au>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Joerg Roedel <jroedel@suse.de>
    Link: https://lkml.kernel.org/r/20190102215655.7A69518C@viggo.jf.intel.com
    a31e184e
mmu_context.h 9.96 KB