[PATCH v2] tpm: only set efi_tpm_final_log_size after successful event log parsing

[Jerry Snitselaar <jsnitsel@redhat.com>]

If __calc_tpm2_event_size fails to parse an event it will return 0,
resulting tpm2_calc_event_log_size returning -1. Currently there is
no check of this return value, and efi_tpm_final_log_size can end up
being set to this negative value resulting in a panic like the
the one given below.

This has been reported with a number of systems now from different
vendors. In the case of the system I have access to the hash algorithm
id associated with an event isn't in the TCG registry, and a match
isn't found when walking the digest sizes array resulting in 0 being
returned by __calc_tpm2_event_size.  There are a number of other
points in __calc_tpm2_event_size where it could potentially return 0
and trigger the same outcome.

[    0.774340] BUG: unable to handle page fault for address: ffffbc8fc00866ad
[    0.774788] #PF: supervisor read access in kernel mode
[    0.774788] #PF: error_code(0x0000) - not-present page
[    0.774788] PGD 107d36067 P4D 107d36067 PUD 107d37067 PMD 107d38067 PTE 0
[    0.774788] Oops: 0000 [#1] SMP PTI
[    0.774788] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.3.0-0.rc2.1.elrdy.x86_64 #1
[    0.774788] Hardware name: LENOVO 20HGS22D0W/20HGS22D0W, BIOS N1WET51W (1.30 ) 09/14/2018
[    0.774788] RIP: 0010:memcpy_erms+0x6/0x10
[    0.774788] Code: 90 90 90 90 eb 1e 0f 1f 00 48 89 f8 48 89 d1 48 c1 e9 03 83 e2 07 f3 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1 <f3> a4 c3 0f 1f 80 00 00 00 00 48 89 f8 48 83 fa 20 72 7e 40 38 fe
[    0.774788] RSP: 0000:ffffbc8fc0073b30 EFLAGS: 00010286
[    0.774788] RAX: ffff9b1fc7c5b367 RBX: ffff9b1fc8390000 RCX: ffffffffffffe962
[    0.774788] RDX: ffffffffffffe962 RSI: ffffbc8fc00866ad RDI: ffff9b1fc7c5b367
[    0.774788] RBP: ffff9b1c10ca7018 R08: ffffbc8fc0085fff R09: 8000000000000063
[    0.774788] R10: 0000000000001000 R11: 000fffffffe00000 R12: 0000000000003367
[    0.774788] R13: ffff9b1fcc47c010 R14: ffffbc8fc0085000 R15: 0000000000000002
[    0.774788] FS:  0000000000000000(0000) GS:ffff9b1fce200000(0000) knlGS:0000000000000000
[    0.774788] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.774788] CR2: ffffbc8fc00866ad CR3: 000000029f60a001 CR4: 00000000003606f0
[    0.774788] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    0.774788] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[    0.774788] Call Trace:
[    0.774788]  tpm_read_log_efi+0x156/0x1a0
[    0.774788]  tpm_bios_log_setup+0xc8/0x190
[    0.774788]  tpm_chip_register+0x50/0x1c0
[    0.774788]  tpm_tis_core_init.cold.9+0x28c/0x466
[    0.774788]  tpm_tis_plat_probe+0xcc/0xea
[    0.774788]  platform_drv_probe+0x35/0x80
[    0.774788]  really_probe+0xef/0x390
[    0.774788]  driver_probe_device+0xb4/0x100
[    0.774788]  device_driver_attach+0x4f/0x60
[    0.774788]  __driver_attach+0x86/0x140
[    0.774788]  ? device_driver_attach+0x60/0x60
[    0.774788]  bus_for_each_dev+0x76/0xc0
[    0.774788]  ? klist_add_tail+0x3b/0x70
[    0.774788]  bus_add_driver+0x14a/0x1e0
[    0.774788]  ? tpm_init+0xea/0xea
[    0.774788]  ? do_early_param+0x8e/0x8e
[    0.774788]  driver_register+0x6b/0xb0
[    0.774788]  ? tpm_init+0xea/0xea
[    0.774788]  init_tis+0x86/0xd8
[    0.774788]  ? do_early_param+0x8e/0x8e
[    0.774788]  ? driver_register+0x94/0xb0
[    0.774788]  do_one_initcall+0x46/0x1e4
[    0.774788]  ? do_early_param+0x8e/0x8e
[    0.774788]  kernel_init_freeable+0x199/0x242
[    0.774788]  ? rest_init+0xaa/0xaa
[    0.774788]  kernel_init+0xa/0x106
[    0.774788]  ret_from_fork+0x35/0x40
[    0.774788] Modules linked in:
[    0.774788] CR2: ffffbc8fc00866ad
[    0.774788] ---[ end trace 42930799f8d6eaea ]---
[    0.774788] RIP: 0010:memcpy_erms+0x6/0x10
[    0.774788] Code: 90 90 90 90 eb 1e 0f 1f 00 48 89 f8 48 89 d1 48 c1 e9 03 83 e2 07 f3 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1 <f3> a4 c3 0f 1f 80 00 00 00 00 48 89 f8 48 83 fa 20 72 7e 40 38 fe
[    0.774788] RSP: 0000:ffffbc8fc0073b30 EFLAGS: 00010286
[    0.774788] RAX: ffff9b1fc7c5b367 RBX: ffff9b1fc8390000 RCX: ffffffffffffe962
[    0.774788] RDX: ffffffffffffe962 RSI: ffffbc8fc00866ad RDI: ffff9b1fc7c5b367
[    0.774788] RBP: ffff9b1c10ca7018 R08: ffffbc8fc0085fff R09: 8000000000000063
[    0.774788] R10: 0000000000001000 R11: 000fffffffe00000 R12: 0000000000003367
[    0.774788] R13: ffff9b1fcc47c010 R14: ffffbc8fc0085000 R15: 0000000000000002
[    0.774788] FS:  0000000000000000(0000) GS:ffff9b1fce200000(0000) knlGS:0000000000000000
[    0.774788] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.774788] CR2: ffffbc8fc00866ad CR3: 000000029f60a001 CR4: 00000000003606f0
[    0.774788] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    0.774788] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[    0.774788] Kernel panic - not syncing: Fatal exception
[    0.774788] Kernel Offset: 0x1d000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[    0.774788] ---[ end Kernel panic - not syncing: Fatal exception ]---

Also __calc_tpm2_event_size returns a size of 0 when it fails
to parse an event, so update function documentation to reflect this.

Fixes: c46f3405692de ("tpm: Reserve the TPM final events table")
Cc: linux-efi@vger.kernel.org
Cc: linux-integrity@vger.kernel.org
Cc: stable@vger.kernel.org
Cc: Matthew Garrett <mjg59@google.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>
---
v2: added FW_BUG to pr_err, and renamed label to out_calc. Also updated comment
    for __calc_tpm2_event_size to properly state that returning 0 is failure.

 drivers/firmware/efi/tpm.c   | 11 ++++++++---
 include/linux/tpm_eventlog.h |  2 +-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
index 1d3f5ca3eaaf..284da9242a4f 100644
--- a/drivers/firmware/efi/tpm.c
+++ b/drivers/firmware/efi/tpm.c
@@ -40,8 +40,7 @@ int __init efi_tpm_eventlog_init(void)
 {
 	struct linux_efi_tpm_eventlog *log_tbl;
 	struct efi_tcg2_final_events_table *final_tbl;
-	unsigned int tbl_size;
-	int ret = 0;
+	int tbl_size, ret = 0;
 
 	if (efi.tpm_log == EFI_INVALID_TABLE_ADDR) {
 		/*
@@ -80,11 +79,17 @@ int __init efi_tpm_eventlog_init(void)
 					    + sizeof(final_tbl->nr_events),
 					    final_tbl->nr_events,
 					    log_tbl->log);
+	if (tbl_size < 0) {
+		pr_err(FW_BUG "Failed to parse event in TPM Final Event log\n");
+		goto out_calc;
+	}
+
 	memblock_reserve((unsigned long)final_tbl,
 			 tbl_size + sizeof(*final_tbl));
-	early_memunmap(final_tbl, sizeof(*final_tbl));
 	efi_tpm_final_log_size = tbl_size;
 
+out_calc:
+	early_memunmap(final_tbl, sizeof(*final_tbl));
 out:
 	early_memunmap(log_tbl, sizeof(*log_tbl));
 	return ret;
diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h
index 63238c84dc0b..7388ef0ce483 100644
--- a/include/linux/tpm_eventlog.h
+++ b/include/linux/tpm_eventlog.h
@@ -152,7 +152,7 @@ struct tcg_algorithm_info {
  * total. Once we've done this we know the offset of the data length field,
  * and can calculate the total size of the event.
  *
- * Return: size of the event on success, <0 on failure
+ * Return: size of the event on success, 0 on failure
  */
 
 static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
-- 
2.23.0