Commit ffc2760b authored Jan 03, 2020 by Ard Biesheuvel Committed by Ingo Molnar Jan 10, 2020

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



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: 5b83683f ("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>

parent 6cfcd6f0

arch/x86/platform/efi/efi.c

+7 −6

Original line number	Diff line number	Diff line
		@@ -541,7 +541,6 @@ 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 \|\|
		@@ -566,14 +565,16 @@ 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,

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