Userspace can supply an iova and uptr such that the target iova alignment
becomes really big and ALIGN() overflows which corrupts the selected area
range during allocation. CONFIG_IOMMUFD_TEST can detect this:

   WARNING: CPU: 1 PID: 5092 at drivers/iommu/iommufd/io_pagetable.c:268 iopt_alloc_area_pages drivers/iommu/iommufd/io_pagetable.c:268 [inline]
   WARNING: CPU: 1 PID: 5092 at drivers/iommu/iommufd/io_pagetable.c:268 iopt_map_pages+0xf95/0x1050 drivers/iommu/iommufd/io_pagetable.c:352
   Modules linked in:
   CPU: 1 PID: 5092 Comm: syz-executor294 Not tainted 6.10.0-rc5-syzkaller-00294-g3ffea9a7 #0
   Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
   RIP: 0010:iopt_alloc_area_pages drivers/iommu/iommufd/io_pagetable.c:268 [inline]
   RIP: 0010:iopt_map_pages+0xf95/0x1050 drivers/iommu/iommufd/io_pagetable.c:352
   Code: fc e9 a4 f3 ff ff e8 1a 8b 4c fc 41 be e4 ff ff ff e9 8a f3 ff ff e8 0a 8b 4c fc 90 0f 0b 90 e9 37 f5 ff ff e8 fc 8a 4c fc 90 <0f> 0b 90 e9 68 f3 ff ff 48 c7 c1 ec 82 ad 8f 80 e1 07 80 c1 03 38
   RSP: 0018:ffffc90003ebf9e0 EFLAGS: 00010293
   RAX: ffffffff85499fa4 RBX: 00000000ffffffef RCX: ffff888079b49e00
   RDX: 0000000000000000 RSI: 00000000ffffffef RDI: 0000000000000000
   RBP: ffffc90003ebfc50 R08: ffffffff85499b30 R09: ffffffff85499942
   R10: 0000000000000002 R11: ffff888079b49e00 R12: ffff8880228e0010
   R13: 0000000000000000 R14: 1ffff920007d7f68 R15: ffffc90003ebfd00
   FS:  000055557d760380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
   CR2: 00000000005fdeb8 CR3: 000000007404a000 CR4: 00000000003506f0
   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
   Call Trace:
    <TASK>
    iommufd_ioas_copy+0x610/0x7b0 drivers/iommu/iommufd/ioas.c:274
    iommufd_fops_ioctl+0x4d9/0x5a0 drivers/iommu/iommufd/main.c:421
    vfs_ioctl fs/ioctl.c:51 [inline]
    __do_sys_ioctl fs/ioctl.c:907 [inline]
    __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
    do_syscall_x64 arch/x86/entry/common.c:52 [inline]
    do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

Cap the automatic alignment to the huge page size, which is probably a
better idea overall. Huge automatic alignments can fragment and chew up
the available IOVA space without any reason.

Link: https://patch.msgid.link/r/0-v1-8009738b9891+1f7-iommufd_align_overflow_jgg@nvidia.com
Cc: stable@vger.kernel.org
Fixes: 51fe6141 ("iommufd: Data structure to provide IOVA to PFN mapping")
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reported-by: syzbot+16073ebbc4c64b819b47@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/000000000000388410061a74f014@google.comSigned-off-by: Jason Gunthorpe <jgg@nvidia.com>