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

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[ 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>
This commit is contained in:
Ard Biesheuvel 2020-01-03 12:39:37 +01:00 committed by prashantpaddune
parent 8081f12140
commit 19227b5089
1 changed files with 7 additions and 6 deletions
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13
arch/x86/platform/efi/efi.c
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@ -465,7 +465,6 @@ 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 ||
@ -490,14 +489,16 @@ 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,