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Subject[PATCH 7/8] x86, microcode, intel: forbid some incorrect metadata
Date
Ensure that both the microcode data_size and total_size fields are a
multiple of the dword size (4 bytes). The Intel SDM vol 3A (order code
253668-051US, June 2014) requires this to be true, and the driver code
assumes it will be true.

Add a comment to the code stating that it is best if we continue to
refrain from ensuring that total_size is a multiple of 1024 bytes. The
reason to never add that check is non-obvious.

Refuse a microcode with a revision of zero, we reserve that for the
factory-provided microcode.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
---
arch/x86/kernel/cpu/microcode/intel_lib.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel_lib.c b/arch/x86/kernel/cpu/microcode/intel_lib.c
index 95c2d19..050cd4f 100644
--- a/arch/x86/kernel/cpu/microcode/intel_lib.c
+++ b/arch/x86/kernel/cpu/microcode/intel_lib.c
@@ -61,12 +61,22 @@ int microcode_sanity_check(void *mc, int print_err)
total_size = get_totalsize(mc_header);
data_size = get_datasize(mc_header);

- if (data_size + MC_HEADER_SIZE > total_size) {
+ if ((data_size % DWSIZE) || (total_size % DWSIZE) ||
+ (data_size + MC_HEADER_SIZE > total_size)) {
if (print_err)
- pr_err("error! Bad data size in microcode data file\n");
+ pr_err("error! Bad data size or total size in microcode data file\n");
return -EINVAL;
}

+ /*
+ * DO NOT add a check for total_size to be a multiple of 1024.
+ *
+ * While there is a requirement that total_size be a multiple of 1024
+ * (Intel SDM vol 3A, section 9.11.1, table 9-6, page 9-29), it clashes
+ * with the "delete extended signature table" procedure described for
+ * the Checksum[n] field in the same table 9-6, at page 9-30).
+ */
+
ext_table_size = total_size - (MC_HEADER_SIZE + data_size);
if (ext_table_size) {
if ((ext_table_size < EXT_HEADER_SIZE)
@@ -84,6 +94,13 @@ int microcode_sanity_check(void *mc, int print_err)
ext_sigcount = ext_header->count;
}

+ /* check some of the metadata */
+ if (mc_header->rev == 0) { /* reserved for silicon microcode */
+ if (print_err)
+ pr_err("error! Restricted revision 0 in microcode data file\n");
+ return -EINVAL;
+ }
+
/* check extended table checksum */
if (ext_table_size) {
int ext_table_sum = 0;
--
1.7.10.4


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