linux-kernel - [PATCH v2 1/4] efi: stmm: Fix incorrect buffer allocation method

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Message-ID: <c7ddb74b514c36ed4f612bc2125245c1f68c0a4d.1755969734.git.jan.kiszka@siemens.com>
Date: Sat, 23 Aug 2025 19:22:11 +0200
From: Jan Kiszka <jan.kiszka@...mens.com>
To: Ard Biesheuvel <ardb@...nel.org>,
	Masahisa Kojima <kojima.masahisa@...ionext.com>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc: linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Sumit Garg <sumit.garg@...nel.org>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Hua Qian Li <huaqian.li@...mens.com>
Subject: [PATCH v2 1/4] efi: stmm: Fix incorrect buffer allocation method

From: Jan Kiszka <jan.kiszka@...mens.com>

The communication buffer allocated by setup_mm_hdr is later on passed to
tee_shm_register_kernel_buf. The latter expects those buffers to be
contiguous pages, but setup_mm_hdr just uses kmalloc. That can cause
various corruptions or BUGs, specifically since 9aec2fb0fd5e, though it
was broken before as well.

Fix this by using alloc_pages_exact instead of kmalloc.

Fixes: c44b6be62e8d ("efi: Add tee-based EFI variable driver")
Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
---
 drivers/firmware/efi/stmm/tee_stmm_efi.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/firmware/efi/stmm/tee_stmm_efi.c b/drivers/firmware/efi/stmm/tee_stmm_efi.c
index f741ca279052..e15d11ed165e 100644
--- a/drivers/firmware/efi/stmm/tee_stmm_efi.c
+++ b/drivers/firmware/efi/stmm/tee_stmm_efi.c
@@ -143,6 +143,10 @@ static efi_status_t mm_communicate(u8 *comm_buf, size_t payload_size)
 	return var_hdr->ret_status;
 }
 
+#define COMM_BUF_SIZE(__payload_size)	(MM_COMMUNICATE_HEADER_SIZE + \
+					 MM_VARIABLE_COMMUNICATE_SIZE + \
+					 (__payload_size))
+
 /**
  * setup_mm_hdr() -	Allocate a buffer for StandAloneMM and initialize the
  *			header data.
@@ -173,9 +177,8 @@ static void *setup_mm_hdr(u8 **dptr, size_t payload_size, size_t func,
 		return NULL;
 	}
 
-	comm_buf = kzalloc(MM_COMMUNICATE_HEADER_SIZE +
-				   MM_VARIABLE_COMMUNICATE_SIZE + payload_size,
-			   GFP_KERNEL);
+	comm_buf = alloc_pages_exact(COMM_BUF_SIZE(payload_size),
+				     GFP_KERNEL | __GFP_ZERO);
 	if (!comm_buf) {
 		*ret = EFI_OUT_OF_RESOURCES;
 		return NULL;
@@ -239,7 +242,7 @@ static efi_status_t get_max_payload(size_t *size)
 	 */
 	*size -= 2;
 out:
-	kfree(comm_buf);
+	free_pages_exact(comm_buf, COMM_BUF_SIZE(payload_size));
 	return ret;
 }
 
@@ -282,7 +285,7 @@ static efi_status_t get_property_int(u16 *name, size_t name_size,
 	memcpy(var_property, &smm_property->property, sizeof(*var_property));
 
 out:
-	kfree(comm_buf);
+	free_pages_exact(comm_buf, COMM_BUF_SIZE(payload_size));
 	return ret;
 }
 
@@ -347,7 +350,7 @@ static efi_status_t tee_get_variable(u16 *name, efi_guid_t *vendor,
 	memcpy(data, (u8 *)var_acc->name + var_acc->name_size,
 	       var_acc->data_size);
 out:
-	kfree(comm_buf);
+	free_pages_exact(comm_buf, COMM_BUF_SIZE(payload_size));
 	return ret;
 }
 
@@ -404,7 +407,7 @@ static efi_status_t tee_get_next_variable(unsigned long *name_size,
 	memcpy(name, var_getnext->name, var_getnext->name_size);
 
 out:
-	kfree(comm_buf);
+	free_pages_exact(comm_buf, COMM_BUF_SIZE(payload_size));
 	return ret;
 }
 
@@ -467,7 +470,7 @@ static efi_status_t tee_set_variable(efi_char16_t *name, efi_guid_t *vendor,
 	ret = mm_communicate(comm_buf, payload_size);
 	dev_dbg(pvt_data.dev, "Set Variable %s %d %lx\n", __FILE__, __LINE__, ret);
 out:
-	kfree(comm_buf);
+	free_pages_exact(comm_buf, COMM_BUF_SIZE(payload_size));
 	return ret;
 }
 
@@ -507,7 +510,7 @@ static efi_status_t tee_query_variable_info(u32 attributes,
 	*max_variable_size = mm_query_info->max_variable_size;
 
 out:
-	kfree(comm_buf);
+	free_pages_exact(comm_buf, COMM_BUF_SIZE(payload_size));
 	return ret;
 }
 
-- 
2.43.0