Re: [PATCH 11/11] x86/ucode/amd: Rework parsing logic in cpu_request_microcode()

From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH 11/11] x86/ucode/amd: Rework parsing logic in cpu_request_microcode()
Date: Tue, 31 Mar 2020 17:07:07 +0200	[thread overview]
Message-ID: <cbb0b2c8-d06b-4b49-f955-dffe002acdae@suse.com> (raw)
In-Reply-To: <20200331100531.4294-12-andrew.cooper3@citrix.com>

On 31.03.2020 12:05, Andrew Cooper wrote:
> @@ -269,55 +265,25 @@ static int apply_microcode(const struct microcode_patch *patch)
>      return 0;
>  }
>  
> -static int scan_equiv_cpu_table(
> -    const void *data,
> -    size_t size_left,
> -    size_t *offset)
> +static int scan_equiv_cpu_table(const struct container_equiv_table *et)
>  {
>      const struct cpu_signature *sig = &this_cpu(cpu_sig);
> -    const struct mpbhdr *mpbuf;
> -    const struct equiv_cpu_entry *eq;
> -    unsigned int i, nr;
> -
> -    if ( size_left < (sizeof(*mpbuf) + 4) ||
> -         (mpbuf = data + *offset + 4,
> -          size_left - sizeof(*mpbuf) - 4 < mpbuf->len) )
> -    {
> -        printk(XENLOG_WARNING "microcode: No space for equivalent cpu table\n");
> -        return -EINVAL;
> -    }
> -
> -    *offset += mpbuf->len + CONT_HDR_SIZE;	/* add header length */
> -
> -    if ( mpbuf->type != UCODE_EQUIV_CPU_TABLE_TYPE )
> -    {
> -        printk(KERN_ERR "microcode: Wrong microcode equivalent cpu table type field\n");
> -        return -EINVAL;
> -    }
> -
> -    if ( mpbuf->len == 0 || mpbuf->len % sizeof(*eq) ||
> -         (eq = (const void *)mpbuf->data,
> -          nr = mpbuf->len / sizeof(*eq),
> -          eq[nr - 1].installed_cpu) )

Did this last check get lost? I can't seem to be able to identify
any possible replacement.

>  static struct microcode_patch *cpu_request_microcode(const void *buf, size_t size)
>  {
>      const struct microcode_patch *saved = NULL;
>      struct microcode_patch *patch = NULL;
> -    size_t offset = 0, saved_size = 0;
> +    size_t saved_size = 0;
>      int error = 0;
> -    unsigned int cpu = smp_processor_id();
> -    const struct cpu_signature *sig = &per_cpu(cpu_sig, cpu);
>  
> -    if ( size < 4 ||
> -         *(const uint32_t *)buf != UCODE_MAGIC )
> +    while ( size )
>      {
> -        printk(KERN_ERR "microcode: Wrong microcode patch file magic\n");
> -        error = -EINVAL;
> -        goto out;
> -    }
> -
> -    /*
> -     * Multiple container file support:
> -     * 1. check if this container file has equiv_cpu_id match
> -     * 2. If not, fast-fwd to next container file
> -     */
> -    while ( offset < size )
> -    {
> -        error = scan_equiv_cpu_table(buf, size - offset, &offset);
> -
> -        if ( !error || error != -ESRCH )
> -            break;
> +        const struct container_equiv_table *et;
> +        bool skip_ucode;
>  
> -        error = container_fast_forward(buf, size - offset, &offset);
> -        if ( error == -ENODATA )
> +        if ( size < 4 || *(const uint32_t *)buf != UCODE_MAGIC )
>          {
> -            ASSERT(offset == size);
> +            printk(XENLOG_ERR "microcode: Wrong microcode patch file magic\n");
> +            error = -EINVAL;
>              break;
>          }
> -        if ( error )
> +
> +        /* Move over UCODE_MAGIC. */
> +        buf  += 4;
> +        size -= 4;
> +
> +        if ( size < sizeof(*et) ||
> +             (et = buf)->type != UCODE_EQUIV_CPU_TABLE_TYPE ||
> +             size - sizeof(*et) < et->len ||
> +             et->len % sizeof(et->eq[0]) )
>          {
> -            printk(KERN_ERR "microcode: CPU%d incorrect or corrupt container file\n"
> -                   "microcode: Failed to update patch level. "
> -                   "Current lvl:%#x\n", cpu, sig->rev);
> +            printk(XENLOG_ERR "microcode: Bad equivalent cpu table\n");
> +            error = -EINVAL;
>              break;
>          }
> -    }
>  
> -    if ( error )
> -    {
> -        /*
> -         * -ENODATA here means that the blob was parsed fine but no matching
> -         * ucode was found. Don't return it to the caller.
> -         */
> -        if ( error == -ENODATA )
> -            error = 0;
> -
> -        goto out;
> -    }
> +        /* Move over the Equiv table. */
> +        buf  += sizeof(*et) + et->len;
> +        size -= sizeof(*et) + et->len;
> +
> +        error = scan_equiv_cpu_table(et);
> +        if ( error && error != -ESRCH )
> +            break;

With this the only non-zero value left for error is -ESRCH.
Hence ...

> +        /* -ESRCH means no applicable microcode in this container. */
> +        skip_ucode = error == -ESRCH;

... perhaps omit the "== -ESRCH" here, moving the comment up
ahead of the if()?

Jan