On Sat, Sep 6, 2014 at 11:09 PM, Mantas Mikulėnas <grawity@xxxxxxxxx> wrote:
> On Sat, Sep 6, 2014 at 1:16 AM, Matt Fleming <matt@xxxxxxxxxxxxxxxxx> wrote:
>> On Thu, 04 Sep, at 01:59:05PM, H. Peter Anvin wrote:
>>>
>>> I am fine with this patch, but at the same time I do want to note that
>>> there is an alternative to double-buffer the patch and/or (if that
>>> applies to the buggy BIOS) round up the size of the target buffer.
>>
>> I took a whack at the double-buffer strategy, and I think the patch is
>> conceptually pretty straight forward.
>>
>> Could someone try out the following patch? It works around the problem
>> on my ASUS machine.
>>
>> ---
>>
>> From 89e7fdaeb04f79d9834678e486215974986d4ac8 Mon Sep 17 00:00:00 2001
>> From: Matt Fleming <matt.fleming@xxxxxxxxx>
>> Date: Fri, 5 Sep 2014 23:15:11 +0100
>> Subject: [PATCH] x86/efi: Workaround firmware bug with double-buffer read
>> MIME-Version: 1.0
>> Content-Type: text/plain; charset=UTF-8
>> Content-Transfer-Encoding: 8bit
>>
>> Mantas found that after commit 4bf7111f5016 ("x86/efi: Support initrd
>> loaded above 4G"), the kernel freezes at the earliest possible moment
>> when trying to boot via UEFI on Asus laptop.
>>
>> The cause of the freeze appears to be a firmware bug when reading file
>> data into buffers above 4GB, though the exact reason is unknown. Mantas
>> reports that the hang can be avoided if the file size is a multiple of
>> 512 bytes, but I've seen some ASUS firmware simply corrupting the file
>> data rather than freezing.
>>
>> Since the bug has only been reported when reading into a buffer above
>> 4GB, we can workaround the problem by doing a double-buffer read, where
>> we read a partial file chunk into a buffer < 4GB then copy it to the
>> buffer (potentially) above 4GB.
>>
>> Laszlo fixed an issue in the upstream EDK2 DiskIO code in Aug 2013 which
>> may possibly be related, commit 4e39b75e ("MdeModulePkg/DiskIoDxe: fix
>> source/destination pointer of overrun transfer"). Whatever the cause,
>> it's unlikely that a fix will be forthcoming from the vendor, hence the
>> workaround.
>>
>> Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
>> Cc: Laszlo Ersek <lersek@xxxxxxxxxx>
>> Reported-by: Mantas Mikulėnas <grawity@xxxxxxxxx>
>> Reported-by: Harald Hoyer <harald@xxxxxxxxxx>
>> Signed-off-by: Matt Fleming <matt.fleming@xxxxxxxxx>
>> ---
>> drivers/firmware/efi/libstub/efi-stub-helper.c | 28 ++++++++++++++++++++++++--
>> 1 file changed, 26 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
>> index 32d5cca30f49..470793ce2617 100644
>> --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
>> +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
>> @@ -297,6 +297,7 @@ efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
>> {
>> struct file_info *files;
>> unsigned long file_addr;
>> + unsigned long chunkbuf;
>> u64 file_size_total;
>> efi_file_handle_t *fh = NULL;
>> efi_status_t status;
>> @@ -416,6 +417,24 @@ efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
>> goto free_file_total;
>> }
>>
>> + /*
>> + * Allocate a bounce buffer below 4GB.
>> + *
>> + * Some firmware implementations cannot perform file
>> + * reads into buffers above 4G and at best corrupt the
>> + * buffer, at worst they hang completely.
>> + *
>> + * Pass chunkbuf to the firmware to perform reads in
>> + * chunksize bytes and copy them to the target buffer
>> + * 'file_addr'.
>> + */
>> + status = efi_high_alloc(sys_table_arg, EFI_READ_CHUNK_SIZE,
>> + 0x1000, &chunkbuf, 0xffffffff);
>> + if (status != EFI_SUCCESS) {
>> + pr_efi_err(sys_table_arg, "Failed to alloc file chunk buffer\n");
>> + goto free_chunk;
>> + }
>> +
>> addr = file_addr;
>> for (j = 0; j < nr_files; j++) {
>> unsigned long size;
>> @@ -430,11 +449,13 @@ efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
>>
>> status = efi_file_read(files[j].handle,
>> &chunksize,
>> - (void *)addr);
>> + (void *)chunkbuf);
>> if (status != EFI_SUCCESS) {
>> pr_efi_err(sys_table_arg, "Failed to read file\n");
>> - goto free_file_total;
>> + goto free_chunk;
>> }
>> +
>> + memcpy((void *)addr, (void *)chunkbuf, chunksize);
>> addr += chunksize;
>> size -= chunksize;
>> }
>> @@ -442,6 +463,7 @@ efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
>> efi_file_close(files[j].handle);
>> }
>>
>> + efi_free(sys_table_arg, EFI_READ_CHUNK_SIZE, chunkbuf);
>> }
>>
>> efi_call_early(free_pool, files);
>> @@ -451,6 +473,8 @@ efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
>>
>> return status;
>>
>> +free_chunk:
>> + efi_free(sys_table_arg, EFI_READ_CHUNK_SIZE, chunkbuf);
>> free_file_total:
>> efi_free(sys_table_arg, file_size_total, file_addr);
>>
>> --
>> 1.9.3
>>
>> --
>> Matt Fleming, Intel Open Source Technology Center
>
> Finally got around to testing the patches here. Sorry for no replies earlier.
>
> This seemed like it would work, but... it hangs at the memcpy?...
>
> (If I add a printk before memcpy and a printk after memcpy, I never
> see the second one. I guess that memory location is just cursed, or
> something.)
>
> Going to test Yinghai's 6aacad3513bf now, just in case.
Err, I meant b524e05df6d4 (the one in mfleming/urgent).
--
Mantas Mikulėnas <grawity@xxxxxxxxx>
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