CVE-2023-53630

In the Linux kernel, the following vulnerability has been resolved:

iommufd: Fix unpinning of pages when an access is present

syzkaller found that the calculation of batchlastindex should use 'start_index' since at input to this function the batch is either empty or it has already been adjusted to cross any accesses so it will start at the point we are unmapping from.

Getting this wrong causes the unmap to run over the end of the pages which corrupts pages that were never mapped. In most cases this triggers the num pinned debugging:

WARNING: CPU: 0 PID: 557 at drivers/iommu/iommufd/pages.c:294 __ioptareaunfill_domain+0x152/0x560 Modules linked in: CPU: 0 PID: 557 Comm: repro Not tainted 6.3.0-rc2-eeac8ede1755 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 RIP: 0010:__ioptareaunfilldomain+0x152/0x560 Code: d2 0f ff 44 8b 64 24 54 48 8b 44 24 48 31 ff 44 89 e6 48 89 44 24 38 e8 fc d3 0f ff 45 85 e4 0f 85 eb 01 00 00 e8 0e d2 0f ff <0f> 0b e8 07 d2 0f ff 48 8b 44 24 38 89 5c 24 58 89 18 8b 44 24 54 RSP: 0018:ffffc9000108baf0 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 00000000ffffffff RCX: ffffffff821e3f85 RDX: 0000000000000000 RSI: ffff88800faf0000 RDI: 0000000000000002 RBP: ffffc9000108bd18 R08: 000000000003ca25 R09: 0000000000000014 R10: 000000000003ca00 R11: 0000000000000024 R12: 0000000000000004 R13: 0000000000000801 R14: 00000000000007ff R15: 0000000000000800 FS: 00007f3499ce1740(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020000243 CR3: 00000000179c2001 CR4: 0000000000770ef0 PKRU: 55555554 Call Trace: <TASK> ioptareaunfilldomain+0x32/0x40 iopttableremovedomain+0x23f/0x4c0 iommufddeviceselftestdetach+0x3a/0x90 iommufdselftestdestroy+0x55/0x70 iommufdobjectdestroyuser+0xce/0x130 iommufddestroy+0xa2/0xc0 iommufdfopsioctl+0x206/0x330 __x64sysioctl+0x10e/0x160 dosyscall64+0x3b/0x90 entrySYSCALL64afterhwframe+0x72/0xdc

Also add some useful WARN_ON sanity checks.