[PATCH v5 6/6] x86/microcode/AMD: Check the equivalence table size when scanning it

Maciej S. Szmigiero
2018-04-23T21:34:46Z

Currently, the code scanning the CPU equivalence table read from a
microcode container file assumes that it actually contains a terminating
zero entry.
Let's check also the size of this table to make sure that we don't read
past it in case it actually doesn't.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
---
arch/x86/kernel/cpu/microcode/amd.c | 33 ++++++++++++++++++++++-----------
1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 2df366cc71ce..5ba933ce1d51 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -39,6 +39,7 @@
#include <asm/msr.h>

static struct equiv_cpu_entry *equiv_cpu_table;
+static unsigned int equiv_cpu_table_entries;

/*
* This points to the current valid container of microcode patches which we will
@@ -63,12 +64,18 @@ static u8 amd_ucode_patch[PATCH_MAX_SIZE];
static const char
ucode_path[] __maybe_unused = "kernel/x86/microcode/AuthenticAMD.bin";

-static u16 find_equiv_id(struct equiv_cpu_entry *equiv_table, u32 sig)
+static u16 find_equiv_id(const struct equiv_cpu_entry *equiv_table,
+ unsigned int equiv_table_entries, u32 sig)
{
- for (; equiv_table && equiv_table->installed_cpu; equiv_table++) {
- if (sig == equiv_table->installed_cpu)
- return equiv_table->equiv_cpu;
- }
+ unsigned int i;
+
+ if (!equiv_table)
+ return 0;
+
+ for (i = 0; i < equiv_table_entries && equiv_table[i].installed_cpu;
+ i++)
+ if (sig == equiv_table[i].installed_cpu)
+ return equiv_table[i].equiv_cpu;

return 0;
}
@@ -237,7 +244,8 @@ static size_t parse_container(u8 *ucode, size_t size, struct cont_desc *desc)
eq = (struct equiv_cpu_entry *)(buf + CONTAINER_HDR_SZ);

/* Find the equivalence ID of our CPU in this table: */
- eq_id = find_equiv_id(eq, desc->cpuid_1_eax);
+ eq_id = find_equiv_id(eq, equiv_tbl_len / sizeof(*eq),
+ desc->cpuid_1_eax);

buf += CONTAINER_HDR_SZ;
buf += equiv_tbl_len;
@@ -499,20 +507,21 @@ void reload_ucode_amd(void)
static u16 __find_equiv_id(unsigned int cpu)
{
struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
- return find_equiv_id(equiv_cpu_table, uci->cpu_sig.sig);
+ return find_equiv_id(equiv_cpu_table, equiv_cpu_table_entries,
+ uci->cpu_sig.sig);
}

static u32 find_cpu_family_by_equiv_cpu(u16 equiv_cpu)
{
- int i = 0;
+ unsigned int i;

BUG_ON(!equiv_cpu_table);

- while (equiv_cpu_table[i].equiv_cpu != 0) {
+ for (i = 0; i < equiv_cpu_table_entries &&
+ equiv_cpu_table[i].equiv_cpu != 0; i++)
if (equiv_cpu == equiv_cpu_table[i].equiv_cpu)
return equiv_cpu_table[i].installed_cpu;
- i++;
- }
+
return 0;
}

@@ -697,6 +706,7 @@ static unsigned int install_equiv_cpu_table(const u8 *buf, size_t buf_size)
}

memcpy(equiv_cpu_table, buf + CONTAINER_HDR_SZ, equiv_tbl_len);
+ equiv_cpu_table_entries = equiv_tbl_len / sizeof(struct equiv_cpu_entry);

return equiv_tbl_len;
}
@@ -705,6 +715,7 @@ static void free_equiv_cpu_table(void)
{
vfree(equiv_cpu_table);
equiv_cpu_table = NULL;
+ equiv_cpu_table_entries = 0;
}

static void cleanup(void)