Re: [PATCH v4 11/13] lib/crypto: sha2: Provide functions for zeroizing SHA2 hmac_sha* structures
From: Thomas Huth
Date: Thu Sep 24 2026 - 14:47:22 EST
On 24/09/2026 19.49, Eric Biggers wrote:
On Thu, Sep 24, 2026 at 10:58:06AM -0400, Nathan Chancellor wrote:Yes, thanks, dropping those three patches is the right thing to do right now. I will try to reproduce the problem in the next days and come up with a proper solution (like setting __DISABLE_EXPORTS if that helps...).
Hi Thomas,
On Wed, Sep 16, 2026 at 11:50:13AM +0200, Thomas Huth wrote:
In certain cases crypto code functions need to zeroize their local SHA2
hmac_sha*_key or hmac_sha*_ctx structures after use to avoid leaking
sensitive material on the stack.
Provide hmac_sha*_zeroize_key() and hmac_sha*_zeroize_ctx() helper
functions that can be used with __cleanup() to automatically zeroize
the structure when it goes out of scope.
Reviewed-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
---
include/crypto/sha2.h | 73 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 73 insertions(+)
diff --git a/include/crypto/sha2.h b/include/crypto/sha2.h
index 7bb8fe169daf2..22fbc37ae8407 100644
--- a/include/crypto/sha2.h
+++ b/include/crypto/sha2.h
@@ -7,6 +7,7 @@
#define _CRYPTO_SHA2_H
#include <linux/types.h>
+#include <linux/string.h>
I am seeing a build failure with CONFIG_CFI=y after this patch landed in
-next as commit 09eb210b7deb ("lib/crypto: sha2: Provide functions for
zeroizing SHA2 hmac_sha* structures").
$ printf 'CONFIG_%s=y\n' CFI KEXEC_FILE >kernel/configs/repro.config
$ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 mrproper defconfig repro.config arch/x86/purgatory/
ld.lld: error: undefined symbol: __memset
>>> referenced by string.c
>>> arch/x86/purgatory/purgatory.ro:(__UNIQUE_ID_addressable___memset_5)
ld.lld: error: undefined symbol: __memmove
>>> referenced by string.c
>>> arch/x86/purgatory/purgatory.ro:(__UNIQUE_ID_addressable___memmove_6)
make[6]: *** [arch/x86/purgatory/Makefile:80: arch/x86/purgatory/purgatory.chk] Error 1
...
This comes from the instances of KCFI_REFERENCE in
arch/x86/include/asm/string_64.h. Maybe __DISABLE_EXPORTS should be set
for the full purgatory to avoid this? I am juggling a lot of stuff at
the moment so just this report instead of a full patch.
To fix linux-next, I dropped patches 10-12 of this series. Thomas,
please resend just those once there is a solution.
Thomas