From: Ard Biesheuvel <ardb@kernel.org>
Date: Fri, 3 Jan 2020 11:39:37 +0000 (+0100)
Subject: efi/x86: Map the entire EFI vendor string before copying it
X-Git-Tag: v4.9.215~129
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=7711cb4324b2ab2a20c9cfbd2fdbad248587d5c9;p=platform%2Fkernel%2Flinux-amlogic.git

efi/x86: Map the entire EFI vendor string before copying it

[ Upstream commit ffc2760bcf2dba0dbef74013ed73eea8310cc52c ]

Fix a couple of issues with the way we map and copy the vendor string:
- we map only 2 bytes, which usually works since you get at least a
  page, but if the vendor string happens to cross a page boundary,
  a crash will result
- only call early_memunmap() if early_memremap() succeeded, or we will
  call it with a NULL address which it doesn't like,
- while at it, switch to early_memremap_ro(), and array indexing rather
  than pointer dereferencing to read the CHAR16 characters.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Matthew Garrett <mjg59@google.com>
Cc: linux-efi@vger.kernel.org
Fixes: 5b83683f32b1 ("x86: EFI runtime service support")
Link: https://lkml.kernel.org/r/20200103113953.9571-5-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index b6669d3..f08abdf 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -478,7 +478,6 @@ void __init efi_init(void)
 	efi_char16_t *c16;
 	char vendor[100] = "unknown";
 	int i = 0;
-	void *tmp;
 
 #ifdef CONFIG_X86_32
 	if (boot_params.efi_info.efi_systab_hi ||
@@ -503,14 +502,16 @@ void __init efi_init(void)
 	/*
 	 * Show what we know for posterity
 	 */
-	c16 = tmp = early_memremap(efi.systab->fw_vendor, 2);
+	c16 = early_memremap_ro(efi.systab->fw_vendor,
+				sizeof(vendor) * sizeof(efi_char16_t));
 	if (c16) {
-		for (i = 0; i < sizeof(vendor) - 1 && *c16; ++i)
-			vendor[i] = *c16++;
+		for (i = 0; i < sizeof(vendor) - 1 && c16[i]; ++i)
+			vendor[i] = c16[i];
 		vendor[i] = '\0';
-	} else
+		early_memunmap(c16, sizeof(vendor) * sizeof(efi_char16_t));
+	} else {
 		pr_err("Could not map the firmware vendor!\n");
-	early_memunmap(tmp, 2);
+	}
 
 	pr_info("EFI v%u.%.02u by %s\n",
 		efi.systab->hdr.revision >> 16,