[PATCH v2] crypto: ccp: add check to get PSP master only when PSP is detected

[Brijesh Singh]

Paulian reported the below kernel crash on Ryzen 5 system:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000073
RIP: 0010:.LC0+0x41f/0xa00
RSP: 0018:ffffa9968003bdd0 EFLAGS: 00010002
RAX: ffffffffb113b130 RBX: 0000000000000000 RCX: 00000000000005a7
RDX: 00000000000000ff RSI: ffff8b46dee651a0 RDI: ffffffffb1bd617c
RBP: 0000000000000246 R08: 00000000000251a0 R09: 0000000000000000
R10: ffffd81f11a38200 R11: ffff8b52e8e0a161 R12: ffffffffb19db220
R13: 0000000000000007 R14: ffffffffb17e4888 R15: 5dccd7affc30a31e
FS:  0000000000000000(0000) GS:ffff8b46dee40000(0000) knlGS:0000000000000000
CR2: 0000000000000073 CR3: 000080128120a000 CR4: 00000000003406e0
Call Trace:
 ? sp_get_psp_master_device+0x56/0x80
 ? map_properties+0x540/0x540
 ? psp_pci_init+0x20/0xe0
 ? map_properties+0x540/0x540
 ? sp_mod_init+0x16/0x1a
 ? do_one_initcall+0x4b/0x190
 ? kernel_init_freeable+0x19b/0x23c
 ? rest_init+0xb0/0xb0
 ? kernel_init+0xa/0x100
 ? ret_from_fork+0x22/0x40

Since Ryzen does not support PSP/SEV firmware hence i->psp_data will
NULL in all sp instances. In those cases, 'i' will point to the
list head after list_for_each_entry(). Dereferencing the head will
cause kernel crash.

Add check to call get master device only when PSP/SEV is detected.

Reported-by: Paulian Bogdan Marinca <paulian@xxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
CC: Gary R Hook <gary.hook@xxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---

Changes since v1:

v1 contained a local change I used for triggering the crash on EPYC system.
we do not need those changes in final patch.

 drivers/crypto/ccp/sp-dev.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/crypto/ccp/sp-dev.c b/drivers/crypto/ccp/sp-dev.c
index eb0da6572720..e0459002eb71 100644
--- a/drivers/crypto/ccp/sp-dev.c
+++ b/drivers/crypto/ccp/sp-dev.c
@@ -252,12 +252,12 @@ struct sp_device *sp_get_psp_master_device(void)
 		goto unlock;
 
 	list_for_each_entry(i, &sp_units, entry) {
-		if (i->psp_data)
+		if (i->psp_data && i->get_psp_master_device) {
+			ret = i->get_psp_master_device();
 			break;
+		}
 	}
 
-	if (i->get_psp_master_device)
-		ret = i->get_psp_master_device();
 unlock:
 	write_unlock_irqrestore(&sp_unit_lock, flags);
 	return ret;
-- 
2.14.3