diff mbox series

tpm: Lazily flush auth session when getting random data

Message ID Z8rRRdwlI6JW8RWF@earth.li (mailing list archive)
State New
Headers show
Series tpm: Lazily flush auth session when getting random data | expand

Commit Message

Jonathan McDowell March 7, 2025, 10:58 a.m. UTC 
From: Jonathan McDowell <noodles@meta.com>

Lazy flushing of TPM auth sessions was introduced to speed up IMA
measurments into the TPM. Make use of it in tpm2_get_random as well,
which has the added benefit of not needlessly cleaning up the session
that IMA is using when there are no userspace accesses taking place.

Command trace before for every call:

hwrng (0x00000161): 14 (52965242 ns)
hwrng (0x00000176): 48 (161612432 ns)
hwrng (0x00000165): 10 (2410494 ns)
hwrng (0x0000017B): 117 (70699883 ns)
hwrng (0x0000017B): 117 (70959666 ns)
hwrng (0x00000165): 10 (2756827 ns)

After, with repeated calls showing no setup:

hwrng (0x00000161): 14 (53044582 ns)
hwrng (0x00000176): 48 (160491333 ns)
hwrng (0x00000165): 10 (2408220 ns)
hwrng (0x0000017B): 117 (70695037 ns)
hwrng (0x0000017B): 117 (70994984 ns)
hwrng (0x0000017B): 117 (70195388 ns)
hwrng (0x0000017B): 117 (70973835 ns)

Signed-off-by: Jonathan McDowell <noodles@meta.com>
---
 drivers/char/tpm/tpm2-cmd.c | 1 -
 1 file changed, 1 deletion(-)

Comments

Jarkko Sakkinen March 7, 2025, 4:34 p.m. UTC | #1 
On Fri, Mar 07, 2025 at 10:58:13AM +0000, Jonathan McDowell wrote:
> From: Jonathan McDowell <noodles@meta.com>
> 
> Lazy flushing of TPM auth sessions was introduced to speed up IMA
> measurments into the TPM. Make use of it in tpm2_get_random as well,
> which has the added benefit of not needlessly cleaning up the session
> that IMA is using when there are no userspace accesses taking place.
> 
> Command trace before for every call:
> 
> hwrng (0x00000161): 14 (52965242 ns)
> hwrng (0x00000176): 48 (161612432 ns)
> hwrng (0x00000165): 10 (2410494 ns)
> hwrng (0x0000017B): 117 (70699883 ns)
> hwrng (0x0000017B): 117 (70959666 ns)
> hwrng (0x00000165): 10 (2756827 ns)
> 
> After, with repeated calls showing no setup:
> 
> hwrng (0x00000161): 14 (53044582 ns)
> hwrng (0x00000176): 48 (160491333 ns)
> hwrng (0x00000165): 10 (2408220 ns)
> hwrng (0x0000017B): 117 (70695037 ns)
> hwrng (0x0000017B): 117 (70994984 ns)
> hwrng (0x0000017B): 117 (70195388 ns)
> hwrng (0x0000017B): 117 (70973835 ns)
> 
> Signed-off-by: Jonathan McDowell <noodles@meta.com>
> ---
>  drivers/char/tpm/tpm2-cmd.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index dfdcbd009720..524d802ede26 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -359,7 +359,6 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max)
>  	} while (retries-- && total < max);
>  
>  	tpm_buf_destroy(&buf);
> -	tpm2_end_auth_session(chip);
>  
>  	return total ? total : -EIO;
>  out:
> -- 
> 2.48.1
> 

Thanks for this. It is a good catch! I'll apply this over the weekend
when I apply Arm FF-A driver patches.

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko
diff mbox series

Patch

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index dfdcbd009720..524d802ede26 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -359,7 +359,6 @@  int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max)
 	} while (retries-- && total < max);
 
 	tpm_buf_destroy(&buf);
-	tpm2_end_auth_session(chip);
 
 	return total ? total : -EIO;
 out: