On Wed, 12 Dec 2018, Dave Hansen wrote:
From: Dave Hansen dave.hansen@linux.intel.com
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.
Our creation of new mm's is a bit convoluted. At fork(), the code does:
- memcpy() the parent mm to initialize child
- mm_init() to initalize some select stuff stuff
- dup_mmap() to create true copies that memcpy() did not do right.
For pkeys, we need to preserve two bits of state across a fork: 'execute_only_pkey' and 'pkey_allocation_map'. Those are preserved by the memcpy(), which I thought did the right thing. But, mm_init() calls init_new_context(), which I thought was *only* for execve()-time and overwrites 'execute_only_pkey' and 'pkey_allocation_map' with "new" values. 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: e8c24d3a23a ("x86/pkeys: Allocation/free syscalls") Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@redhat.com Cc: Borislav Petkov bp@alien8.de Cc: "H. Peter Anvin" hpa@zytor.com Cc: x86@kernel.org Cc: Dave Hansen dave.hansen@linux.intel.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 Cc: stable@vger.kernel.org
Reviewed-by: Thomas Gleixner tglx@linutronix.de