linux-kernel - Re: [PATCH] efi: reserve memory for tpm_log only if TPM final events table is valid

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Message-ID: <1a31390d-f452-4d53-84a9-b9fb2af71e4c@gmail.com>
Date: Fri, 30 Aug 2024 22:52:48 +0100
From: Usama Arif <usamaarif642@...il.com>
To: Gregory Price <gourry@...rry.net>
Cc: ardb@...nel.org, linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
 leitao@...ian.org
Subject: Re: [PATCH] efi: reserve memory for tpm_log only if TPM final events
 table is valid



On 30/08/2024 17:49, Usama Arif wrote:
> 
> 
> On 30/08/2024 17:42, Gregory Price wrote:
>> On Fri, Aug 30, 2024 at 10:28:52PM +0100, Usama Arif wrote:
>>> If efi.tpm_log is corrupted, log_tbl->size can be garbage (and
>>> negative). This can result in a large memblock reservation, resulting
>>> in the kernel booting without sufficient memory. Move the memblock
>>> reservation after log_tbl->version check, and check the value of
>>> both tbl_size and memblock_reserve.
>>>
>>> Signed-off-by: Usama Arif <usamaarif642@...il.com>
>>> ---
>>>  drivers/firmware/efi/tpm.c | 16 +++++++++++++---
>>>  1 file changed, 13 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
>>> index e8d69bd548f3..cfc6a065f441 100644
>>> --- a/drivers/firmware/efi/tpm.c
>>> +++ b/drivers/firmware/efi/tpm.c
>>> @@ -59,9 +59,6 @@ int __init efi_tpm_eventlog_init(void)
>>>  		return -ENOMEM;
>>>  	}
>>>  
>>> -	tbl_size = sizeof(*log_tbl) + log_tbl->size;
>>> -	memblock_reserve(efi.tpm_log, tbl_size);
>>> -
>>>  	if (efi.tpm_final_log == EFI_INVALID_TABLE_ADDR) {
>>>  		pr_info("TPM Final Events table not present\n");
>>>  		goto out;
>>
>> The final event table is not present in TCG 1_2 format, but the
>> tpm log still needs to be mapped.  So this change is incorrect for
>> v1_2.
> 
> hmm so we have 
> 
> 	if (efi.tpm_final_log == EFI_INVALID_TABLE_ADDR) {
> 		pr_info("TPM Final Events table not present\n");
> 		goto out;
> 	} else if (log_tbl->version != EFI_TCG2_EVENT_LOG_FORMAT_TCG_2) {
> 		pr_warn(FW_BUG "TPM Final Events table invalid\n");
> 		goto out;
> 	}
> 
> If the format is TCG 1_2, then log_tbl is not used?
> 

Ah its the case that log_tbl->size will be valid, even if its TCG 2.
Got it, Thanks!

> 
>>
>>> @@ -70,6 +67,19 @@ int __init efi_tpm_eventlog_init(void)
>>>  		goto out;
>>>  	}
>>>  
>>> +	tbl_size = sizeof(*log_tbl) + log_tbl->size;
>>> +	if (tbl_size < 0) {
>>> +		pr_err(FW_BUG "Failed to parse event in TPM Final Events Log\n");
>>> +		ret = -EINVAL;
>>> +		goto out;
>>> +	}
>>> +	if (memblock_reserve(efi.tpm_log, tbl_size)) {
>>> +		pr_err("TPM Event Log memblock reserve fails 0x%lx - %x\n",
>>> +		       efi.tpm_log, tbl_size);
>>> +		ret = -ENOMEM;
>>> +		goto out;
>>> +	}
>>> +
>>>  	final_tbl = early_memremap(efi.tpm_final_log, sizeof(*final_tbl));
>>>  
>>>  	if (!final_tbl) {
>>> -- 
>>> 2.43.5
>>>
>