[PATCH] powerpc/pseries: Fix stack corruption in htpe code

[Benjamin Herrenschmidt]

On Thu, 2016-10-06 at 15:33 +0200, Laurent Dufour wrote:
> This commit fixes a stack corruption in the pseries specific code
> dealing
> with the huge pages.

Wow, nice catch !

> In __pSeries_lpar_hugepage_invalidate() the buffer used to pass
> arguments
> to the hypervisor is not large enough. This leads to a stack
> corruption
> where a previously saved register could be corrupted leading to
> unexpected
> result in the caller, like the following panic:
> 
> Oops: Kernel access of bad area, sig: 11 [#1]
> SMP NR_CPUS=2048 NUMA pSeries
> Modules linked in: virtio_balloon ip_tables x_tables autofs4
> virtio_blk 8139too virtio_pci virtio_ring 8139cp virtio
> CPU: 11 PID: 1916 Comm: mmstress Not tainted 4.8.0 #76
> task: c000000005394880 task.stack: c000000005570000
> NIP: c00000000027bf6c LR: c00000000027bf64 CTR: 0000000000000000
> REGS: c000000005573820 TRAP: 0300   Not tainted  (4.8.0)
> MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR: 84822884  XER:
> 20000000
> CFAR: c00000000010a924 DAR: 420000000014e5e0 DSISR: 40000000 SOFTE: 1
> GPR00: c00000000027bf64 c000000005573aa0 c000000000e02800
> c000000004447964
> GPR04: c00000000404de18 c000000004d38810 00000000042100f5
> 00000000f5002104
> GPR08: e0000000f5002104 0000000000000001 042100f5000000e0
> 00000000042100f5
> GPR12: 0000000000002200 c00000000fe02c00 c00000000404de18
> 0000000000000000
> GPR16: c1ffffffffffe7ff 00003fff62000000 420000000014e5e0
> 00003fff63000000
> GPR20: 0008000000000000 c0000000f7014800 0405e600000000e0
> 0000000000010000
> GPR24: c000000004d38810 c000000004447c10 c00000000404de18
> c000000004447964
> GPR28: c000000005573b10 c000000004d38810 00003fff62000000
> 420000000014e5e0
> NIP [c00000000027bf6c] zap_huge_pmd+0x4c/0x470
> LR [c00000000027bf64] zap_huge_pmd+0x44/0x470
> Call Trace:
> [c000000005573aa0] [c00000000027bf64] zap_huge_pmd+0x44/0x470
> (unreliable)
> [c000000005573af0] [c00000000022bbd8] unmap_page_range+0xcf8/0xed0
> [c000000005573c30] [c00000000022c2d4] unmap_vmas+0x84/0x120
> [c000000005573c80] [c000000000235448] unmap_region+0xd8/0x1b0
> [c000000005573d80] [c0000000002378f0] do_munmap+0x2d0/0x4c0
> [c000000005573df0] [c000000000237be4] SyS_munmap+0x64/0xb0
> [c000000005573e30] [c000000000009560] system_call+0x38/0x108
> Instruction dump:
> fbe1fff8 fb81ffe0 7c7f1b78 7ca32b78 7cbd2b78 f8010010 7c9a2378
> f821ffb1
> 7cde3378 4bfffea9 7c7b1b79 41820298 <e87f0000> 48000130 7fa5eb78
> 7fc4f378
> 
> Most of the time, the bug is surfacing in a caller up in the stack
> from
> __pSeries_lpar_hugepage_invalidate() which is quite confusing.
> 
> This bug is pending since v3.11 but was hidden if a caller of the
> caller of __pSeries_lpar_hugepage_invalidate() has pushed the
> corruped
> register (r18 in this case) in the stack and is not using it until
> restoring it. GCC 6.2.0 seems to raise it more frequently.
> 
> This commit also change the definition of the parameter buffer in
> pSeries_lpar_flush_hash_range() to rely on the global define
> PLPAR_HCALL9_BUFSIZE (no functional change here).
> 
> Fixes: 1a5272866f87 ("powerpc: Optimize hugepage invalidate")
> Cc: <stable at vger.kernel.org>
> Cc: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> Signed-off-by: Laurent Dufour <ldufour at linux.vnet.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/lpar.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/lpar.c
> b/arch/powerpc/platforms/pseries/lpar.c
> index 86707e67843f..aa35245d8d6d 100644
> --- a/arch/powerpc/platforms/pseries/lpar.c
> +++ b/arch/powerpc/platforms/pseries/lpar.c
> @@ -393,7 +393,7 @@ static void
> __pSeries_lpar_hugepage_invalidate(unsigned long *slot,
>  					     unsigned long *vpn, int
> count,
>  					     int psize, int ssize)
>  {
> -	unsigned long param[8];
> +	unsigned long param[PLPAR_HCALL9_BUFSIZE];
>  	int i = 0, pix = 0, rc;
>  	unsigned long flags = 0;
>  	int lock_tlbie = !mmu_has_feature(MMU_FTR_LOCKLESS_TLBIE);
> @@ -522,7 +522,7 @@ static void
> pSeries_lpar_flush_hash_range(unsigned long number, int local)
>  	unsigned long flags = 0;
>  	struct ppc64_tlb_batch *batch =
> this_cpu_ptr(&ppc64_tlb_batch);
>  	int lock_tlbie = !mmu_has_feature(MMU_FTR_LOCKLESS_TLBIE);
> -	unsigned long param[9];
> +	unsigned long param[PLPAR_HCALL9_BUFSIZE];
>  	unsigned long hash, index, shift, hidx, slot;
>  	real_pte_t pte;
>  	int psize, ssize;