[6/7] x86/ucode/intel: Clean up microcode_sanity_check()

Commit Message

Andrew Cooper March 23, 2020, 10:17 a.m. UTC

Rewrite the size checks in a way which which doesn't depend on Xen being
compiled as 64bit.

Introduce a check missing from the old code, that total_size is a multiple of
1024 bytes, and drop unnecessarily defines/macros/structures.

No practical change in behaviour.

Signed-off-by: Andrew Cooper <[e-mail]>
---
CC: Jan Beulich <[e-mail]>
CC: Wei Liu <[e-mail]>
CC: Roger Pau Monné <[e-mail]>
---
 xen/arch/x86/cpu/microcode/intel.c | 147 +++++++++++++++----------------------
 1 file changed, 58 insertions(+), 89 deletions(-)

Comments

Jan Beulich March 25, 2020, 2:07 p.m. UTC | #1

On 23.03.2020 11:17, Andrew Cooper wrote:
> Rewrite the size checks in a way which which doesn't depend on Xen being
> compiled as 64bit.

One too many "which"?

> Introduce a check missing from the old code, that total_size is a multiple of
> 1024 bytes,

Where is this documented? The rather brief section in SDM vol 3 doesn't
mention anything like this.

> and drop unnecessarily defines/macros/structures.

unnecessary?

> @@ -160,93 +153,69 @@ static int collect_cpu_info(struct cpu_signature *csig)
>      return 0;
>  }
>  
> +/*
> + * Sanity check a blob which is expected to be a microcode patch.  The 48 byte
> + * header is of a known format, and together with totalsize are within the
> + * bounds of the container.  Everything else is unchecked.
> + */
>  static int microcode_sanity_check(const struct microcode_intel *mc)
>  {
> -    const struct microcode_header_intel *mc_header = &mc->hdr;
> -    const struct extended_sigtable *ext_header = NULL;
> -    const struct extended_signature *ext_sig;
> -    unsigned long total_size, data_size, ext_table_size;
> -    unsigned int ext_sigcount = 0, i;
> -    uint32_t sum, orig_sum;
> -
> -    total_size = get_totalsize(mc_header);
> -    data_size = get_datasize(mc_header);
> -    if ( (data_size + MC_HEADER_SIZE) > total_size )
> -    {
> -        printk(KERN_ERR "microcode: error! "
> -               "Bad data size in microcode data file\n");
> +    const struct extended_sigtable *ext;
> +    unsigned int total_size = get_totalsize(&mc->hdr);
> +    unsigned int data_size = get_datasize(&mc->hdr);
> +    unsigned int i, ext_size;
> +    uint32_t sum, *ptr;
> +
> +    /*
> +     * Total size must be a multiple of 1024 bytes.  Data size and the header
> +     * must fit within it.
> +     */
> +    if ( (total_size & 1023) ||

Personally I'd fine a hex number easier to recognize in cases like
this.

> +         data_size > (total_size - MC_HEADER_SIZE) )
>          return -EINVAL;
> -    }
>  
> -    if ( (mc_header->ldrver != 1) || (mc_header->hdrver != 1) )
> -    {

Ah - you're dropping this check here altogether. As said on the
earlier patch, I think this may more logically go there.

> -        printk(KERN_ERR "microcode: error! "
> -               "Unknown microcode update format\n");

While this printk() was already suggested to be moved, I'm not
convinced dropping others further down is helpful in case of
issues. We'd see just -EINVAL with no further indication of
what was (deemed) wrong.

> +    /* Checksum the main header and data. */
> +    for ( sum = 0, ptr = (uint32_t *)mc;
> +          ptr < (uint32_t *)&mc->data[data_size]; ++ptr )

You're casting away constness here which future compilers may
(legitimately) warn about. (Similarly again further down.)

Jan

Andrew Cooper March 26, 2020, 2:41 p.m. UTC | #2

On 25/03/2020 14:07, Jan Beulich wrote:
>> Introduce a check missing from the old code, that total_size is a multiple of
>> 1024 bytes,
> Where is this documented? The rather brief section in SDM vol 3 doesn't
> mention anything like this.

It is in the middle of the final paragraph of 9.11.1 Microcode Update,
immediately preceding Table 9-7

"The total size field of the microcode update header specifies the
encrypted data size plus the header size; its value must be in multiples
of 1024 bytes (1 KBytes)."

~Andrew

(I've lost count of how many times I've read this chapter over the
course of developing this series...)

Jan Beulich March 26, 2020, 3:02 p.m. UTC | #3

On 26.03.2020 15:41, Andrew Cooper wrote:
> On 25/03/2020 14:07, Jan Beulich wrote:
>>> Introduce a check missing from the old code, that total_size is a multiple of
>>> 1024 bytes,
>> Where is this documented? The rather brief section in SDM vol 3 doesn't
>> mention anything like this.
> 
> It is in the middle of the final paragraph of 9.11.1 Microcode Update,
> immediately preceding Table 9-7
> 
> "The total size field of the microcode update header specifies the
> encrypted data size plus the header size; its value must be in multiples
> of 1024 bytes (1 KBytes)."

Oh, I had looked at 8.8.5 Microcode Update Resources instead,
being surprised it was much less information than I recalled
was available.

Jan

Patch

diff --git a/xen/arch/x86/cpu/microcode/intel.c b/xen/arch/x86/cpu/microcode/intel.c
index bc3bbf139e..2cccf9c26d 100644
--- a/xen/arch/x86/cpu/microcode/intel.c
+++ b/xen/arch/x86/cpu/microcode/intel.c
@@ -65,17 +65,15 @@  struct microcode_intel {
 };
 
 /* microcode format is extended from prescott processors */
-struct extended_signature {
-    unsigned int sig;
-    unsigned int pf;
-    unsigned int cksum;
-};
-
 struct extended_sigtable {
     unsigned int count;
     unsigned int cksum;
     unsigned int reserved[3];
-    struct extended_signature sigs[0];
+    struct {
+        unsigned int sig;
+        unsigned int pf;
+        unsigned int cksum;
+    } sigs[];
 };
 
 struct microcode_patch {
@@ -84,9 +82,6 @@  struct microcode_patch {
 
 #define PPRO_UCODE_DATASIZE     2000
 #define MC_HEADER_SIZE          (sizeof(struct microcode_header_intel))
-#define EXT_HEADER_SIZE         (sizeof(struct extended_sigtable))
-#define EXT_SIGNATURE_SIZE      (sizeof(struct extended_signature))
-#define DWSIZE                  (sizeof(u32))
 
 static uint32_t get_datasize(const struct microcode_header_intel *hdr)
 {
@@ -134,8 +129,6 @@  static bool signature_maches(const struct cpu_signature *cpu_sig,
     return cpu_sig->pf & ucode_pf;
 }
 
-#define exttable_size(et) ((et)->count * EXT_SIGNATURE_SIZE + EXT_HEADER_SIZE)
-
 static int collect_cpu_info(struct cpu_signature *csig)
 {
     uint64_t msr_content;
@@ -160,93 +153,69 @@  static int collect_cpu_info(struct cpu_signature *csig)
     return 0;
 }
 
+/*
+ * Sanity check a blob which is expected to be a microcode patch.  The 48 byte
+ * header is of a known format, and together with totalsize are within the
+ * bounds of the container.  Everything else is unchecked.
+ */
 static int microcode_sanity_check(const struct microcode_intel *mc)
 {
-    const struct microcode_header_intel *mc_header = &mc->hdr;
-    const struct extended_sigtable *ext_header = NULL;
-    const struct extended_signature *ext_sig;
-    unsigned long total_size, data_size, ext_table_size;
-    unsigned int ext_sigcount = 0, i;
-    uint32_t sum, orig_sum;
-
-    total_size = get_totalsize(mc_header);
-    data_size = get_datasize(mc_header);
-    if ( (data_size + MC_HEADER_SIZE) > total_size )
-    {
-        printk(KERN_ERR "microcode: error! "
-               "Bad data size in microcode data file\n");
+    const struct extended_sigtable *ext;
+    unsigned int total_size = get_totalsize(&mc->hdr);
+    unsigned int data_size = get_datasize(&mc->hdr);
+    unsigned int i, ext_size;
+    uint32_t sum, *ptr;
+
+    /*
+     * Total size must be a multiple of 1024 bytes.  Data size and the header
+     * must fit within it.
+     */
+    if ( (total_size & 1023) ||
+         data_size > (total_size - MC_HEADER_SIZE) )
         return -EINVAL;
-    }
 
-    if ( (mc_header->ldrver != 1) || (mc_header->hdrver != 1) )
-    {
-        printk(KERN_ERR "microcode: error! "
-               "Unknown microcode update format\n");
+    /* Checksum the main header and data. */
+    for ( sum = 0, ptr = (uint32_t *)mc;
+          ptr < (uint32_t *)&mc->data[data_size]; ++ptr )
+        sum += *ptr;
+
+    if ( sum != 0 )
         return -EINVAL;
-    }
-    ext_table_size = total_size - (MC_HEADER_SIZE + data_size);
-    if ( ext_table_size )
-    {
-        if ( (ext_table_size < EXT_HEADER_SIZE) ||
-             ((ext_table_size - EXT_HEADER_SIZE) % EXT_SIGNATURE_SIZE) )
-        {
-            printk(KERN_ERR "microcode: error! "
-                   "Small exttable size in microcode data file\n");
-            return -EINVAL;
-        }
-        ext_header = (void *)mc + MC_HEADER_SIZE + data_size;
-        if ( ext_table_size != exttable_size(ext_header) )
-        {
-            printk(KERN_ERR "microcode: error! "
-                   "Bad exttable size in microcode data file\n");
-            return -EFAULT;
-        }
-        ext_sigcount = ext_header->count;
-    }
 
-    /* check extended table checksum */
-    if ( ext_table_size )
-    {
-        uint32_t ext_table_sum = 0;
-        uint32_t *ext_tablep = (uint32_t *)ext_header;
+    /* Look to see if there is an extended signature table. */
+    ext_size = total_size - data_size - MC_HEADER_SIZE;
 
-        i = ext_table_size / DWSIZE;
-        while ( i-- )
-            ext_table_sum += ext_tablep[i];
-        if ( ext_table_sum )
-        {
-            printk(KERN_WARNING "microcode: aborting, "
-                   "bad extended signature table checksum\n");
-            return -EINVAL;
-        }
-    }
+    /* No extended signature table?  All done. */
+    if ( ext_size == 0 )
+        return 0;
 
-    /* calculate the checksum */
-    orig_sum = 0;
-    i = (MC_HEADER_SIZE + data_size) / DWSIZE;
-    while ( i-- )
-        orig_sum += ((uint32_t *)mc)[i];
-    if ( orig_sum )
-    {
-        printk(KERN_ERR "microcode: aborting, bad checksum\n");
+    /*
+     * Check the structure of the extended signature table, ensuring that it
+     * fits exactly in the remaining space.
+     */
+    ext = (void *)&mc->data[data_size];
+    if ( ext_size < sizeof(*ext) ||
+         (ext_size - sizeof(*ext)) % sizeof(ext->sigs[0]) ||
+         (ext_size - sizeof(*ext)) / sizeof(ext->sigs[0]) != ext->count )
         return -EINVAL;
-    }
-    if ( !ext_table_size )
-        return 0;
-    /* check extended signature checksum */
-    for ( i = 0; i < ext_sigcount; i++ )
-    {
-        ext_sig = (void *)ext_header + EXT_HEADER_SIZE +
-            EXT_SIGNATURE_SIZE * i;
-        sum = orig_sum
-            - (mc_header->sig + mc_header->pf + mc_header->cksum)
-            + (ext_sig->sig + ext_sig->pf + ext_sig->cksum);
-        if ( sum )
-        {
-            printk(KERN_ERR "microcode: aborting, bad checksum\n");
+
+    /* Checksum the whole extended signature table. */
+    for ( sum = 0, ptr = (uint32_t *)ext;
+          ptr < (uint32_t *)&ext->sigs[ext->count]; ++ptr )
+        sum += *ptr;
+
+    if ( sum != 0 )
+        return -EINVAL;
+
+    /*
+     * Checksum each indiviudal extended signature as if it had been in the
+     * main header.
+     */
+    sum = mc->hdr.sig + mc->hdr.pf + mc->hdr.cksum;
+    for ( i = 0; i < ext->count; ++i )
+        if ( sum != (ext->sigs[i].sig + ext->sigs[i].pf + ext->sigs[i].cksum) )
             return -EINVAL;
-        }
-    }
+
     return 0;
 }