linux-kernel - [RFC PATCH v2 1/3] powerpc/prom_init: Replace linux,sml-base/sml-size with linux,sml-log

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Message-ID: <20240311132030.1103122-2-stefanb@linux.ibm.com>
Date: Mon, 11 Mar 2024 09:20:28 -0400
From: Stefan Berger <stefanb@...ux.ibm.com>
To: mpe@...erman.id.au, linux-integrity@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Cc: linux-kernel@...r.kernel.org, jarkko@...nel.org, rnsastry@...ux.ibm.com,
        peterhuewe@....de, viparash@...ibm.com, devicetree@...r.kernel.org,
        jsnitsel@...hat.com, Stefan Berger <stefanb@...ux.ibm.com>
Subject: [RFC PATCH v2 1/3] powerpc/prom_init: Replace linux,sml-base/sml-size with linux,sml-log

linux,sml-base holds the address of a buffer with the TPM log. This
buffer may become invalid after a kexec. To avoid accessing an invalid
address or corrupted buffer, embed the whole TPM log in the device tree
property linux,sml-log. This helps to protect the log since it is
properly carried across a kexec soft reboot with both of the kexec
syscalls.

Avoid having the firmware ingest the whole TPM log when calling
prom_setprop but only create the linux,sml-log property as a place holder.
Insert the actual TPM log during the tree flattening phase.

Fixes: 4a727429abec ("PPC64: Add support for instantiating SML from Open Firmware")
Suggested-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
---
 arch/powerpc/kernel/prom_init.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index e67effdba85c..6f7ca72013c2 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -211,6 +211,8 @@ static cell_t __prombss regbuf[1024];
 
 static bool  __prombss rtas_has_query_cpu_stopped;
 
+static u64 __prombss sml_base;
+static u32 __prombss sml_size;
 
 /*
  * Error results ... some OF calls will return "-1" on error, some
@@ -1954,17 +1956,15 @@ static void __init prom_instantiate_sml(void)
 	}
 	prom_printf(" done\n");
 
-	reserve_mem(base, size);
-
-	prom_setprop(ibmvtpm_node, "/vdevice/vtpm", "linux,sml-base",
-		     &base, sizeof(base));
-	prom_setprop(ibmvtpm_node, "/vdevice/vtpm", "linux,sml-size",
-		     &size, sizeof(size));
-
-	prom_debug("sml base     = 0x%llx\n", base);
+	/* Add property now, defer adding log to tree flattening phase */
+	prom_setprop(ibmvtpm_node, "/vdevice/vtpm", "linux,sml-log",
+		     NULL, 0);
 	prom_debug("sml size     = 0x%x\n", size);
 
 	prom_debug("prom_instantiate_sml: end...\n");
+
+	sml_base = base;
+	sml_size = size;
 }
 
 /*
@@ -2645,6 +2645,17 @@ static void __init scan_dt_build_struct(phandle node, unsigned long *mem_start,
 		}
 		prev_name = sstart + soff;
 
+		if (!prom_strcmp("linux,sml-log", pname)) {
+			/* push property head */
+			dt_push_token(OF_DT_PROP, mem_start, mem_end);
+			dt_push_token(sml_size, mem_start, mem_end);
+			dt_push_token(soff, mem_start, mem_end);
+			/* push property content */
+			valp = make_room(mem_start, mem_end, sml_size, 1);
+			memcpy(valp, (void *)sml_base, sml_size);
+			*mem_start = ALIGN(*mem_start, 4);
+			continue;
+		}
 		/* get length */
 		l = call_prom("getproplen", 2, 1, node, pname);
 
-- 
2.43.0