linux-kernel - [PATCH 7/9] efi/libstub/file: merge filename buffers to reduce stack usage

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Message-Id: <20200409130434.6736-8-ardb@kernel.org>
Date:   Thu,  9 Apr 2020 15:04:32 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Borislav Petkov <bp@...e.de>,
        Colin Ian King <colin.king@...onical.com>,
        Gary Lin <glin@...e.com>, Jiri Slaby <jslaby@...e.cz>,
        Sergey Shatunov <me@...k.pw>, Takashi Iwai <tiwai@...e.de>
Subject: [PATCH 7/9] efi/libstub/file: merge filename buffers to reduce stack usage

Arnd reports that commit

  9302c1bb8e47 ("efi/libstub: Rewrite file I/O routine")

reworks the file I/O routines in a way that triggers the following
warning:

  drivers/firmware/efi/libstub/file.c:240:1: warning: the frame size
            of 1200 bytes is larger than 1024 bytes [-Wframe-larger-than=]

We can work around this issue dropping an instance of efi_char16_t[256]
from the stack frame, and reusing the 'filename' field of the file info
struct that we use to obtain file information from EFI (which contains
the filename even though we already know it since we used it to open
the file in the first place)

Reported-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 drivers/firmware/efi/libstub/file.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/drivers/firmware/efi/libstub/file.c b/drivers/firmware/efi/libstub/file.c
index d4c7e5f59d2c..ea66b1f16a79 100644
--- a/drivers/firmware/efi/libstub/file.c
+++ b/drivers/firmware/efi/libstub/file.c
@@ -29,30 +29,31 @@
  */
 #define EFI_READ_CHUNK_SIZE	SZ_1M
 
+struct finfo {
+	efi_file_info_t info;
+	efi_char16_t	filename[MAX_FILENAME_SIZE];
+};
+
 static efi_status_t efi_open_file(efi_file_protocol_t *volume,
-				  efi_char16_t *filename_16,
+				  struct finfo *fi,
 				  efi_file_protocol_t **handle,
 				  unsigned long *file_size)
 {
-	struct {
-		efi_file_info_t info;
-		efi_char16_t	filename[MAX_FILENAME_SIZE];
-	} finfo;
 	efi_guid_t info_guid = EFI_FILE_INFO_ID;
 	efi_file_protocol_t *fh;
 	unsigned long info_sz;
 	efi_status_t status;
 
-	status = volume->open(volume, &fh, filename_16, EFI_FILE_MODE_READ, 0);
+	status = volume->open(volume, &fh, fi->filename, EFI_FILE_MODE_READ, 0);
 	if (status != EFI_SUCCESS) {
 		pr_efi_err("Failed to open file: ");
-		efi_char16_printk(filename_16);
+		efi_char16_printk(fi->filename);
 		efi_printk("\n");
 		return status;
 	}
 
-	info_sz = sizeof(finfo);
-	status = fh->get_info(fh, &info_guid, &info_sz, &finfo);
+	info_sz = sizeof(struct finfo);
+	status = fh->get_info(fh, &info_guid, &info_sz, fi);
 	if (status != EFI_SUCCESS) {
 		pr_efi_err("Failed to get file info\n");
 		fh->close(fh);
@@ -60,7 +61,7 @@ static efi_status_t efi_open_file(efi_file_protocol_t *volume,
 	}
 
 	*handle = fh;
-	*file_size = finfo.info.file_size;
+	*file_size = fi->info.file_size;
 	return EFI_SUCCESS;
 }
 
@@ -146,13 +147,13 @@ static efi_status_t handle_cmdline_files(efi_loaded_image_t *image,
 
 	alloc_addr = alloc_size = 0;
 	do {
-		efi_char16_t filename[MAX_FILENAME_SIZE];
+		struct finfo fi;
 		unsigned long size;
 		void *addr;
 
 		offset = find_file_option(cmdline, cmdline_len,
 					  optstr, optstr_size,
-					  filename, ARRAY_SIZE(filename));
+					  fi.filename, ARRAY_SIZE(fi.filename));
 
 		if (!offset)
 			break;
@@ -166,7 +167,7 @@ static efi_status_t handle_cmdline_files(efi_loaded_image_t *image,
 				return status;
 		}
 
-		status = efi_open_file(volume, filename, &file, &size);
+		status = efi_open_file(volume, &fi, &file, &size);
 		if (status != EFI_SUCCESS)
 			goto err_close_volume;
 
-- 
2.17.1