Hello Shreyansh Chouhan,
The patch 72ff2bf04db2: "crypto: aesni - xts_crypt() return if
walk.nbytes is 0" from Aug 22, 2021, leads to the following
Smatch static checker warning:
arch/x86/crypto/aesni-intel_glue.c:915 xts_crypt()
warn: possible missing kernel_fpu_end()
arch/x86/crypto/aesni-intel_glue.c
839 static int xts_crypt(struct skcipher_request *req, bool encrypt)
840 {
841 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
842 struct aesni_xts_ctx *ctx = crypto_skcipher_ctx(tfm);
843 int tail = req->cryptlen % AES_BLOCK_SIZE;
844 struct skcipher_request subreq;
845 struct skcipher_walk walk;
846 int err;
847
848 if (req->cryptlen < AES_BLOCK_SIZE)
849 return -EINVAL;
850
851 err = skcipher_walk_virt(&walk, req, false);
852 if (!walk.nbytes)
853 return err;
The patch adds this check for "walk.nbytes == 0".
854
855 if (unlikely(tail > 0 && walk.nbytes < walk.total)) {
^^^^^^^^^^^^^^^^^^^^^^^^
But Smatch says that "walk.nbytes" can be set to zero inside this
if statement.
856 int blocks = DIV_ROUND_UP(req->cryptlen, AES_BLOCK_SIZE) - 2;
857
858 skcipher_walk_abort(&walk);
859
860 skcipher_request_set_tfm(&subreq, tfm);
861 skcipher_request_set_callback(&subreq,
862 skcipher_request_flags(req),
863 NULL, NULL);
864 skcipher_request_set_crypt(&subreq, req->src, req->dst,
865 blocks * AES_BLOCK_SIZE, req->iv);
866 req = &subreq;
867
868 err = skcipher_walk_virt(&walk, req, false);
869 if (err)
870 return err;
871 } else {
872 tail = 0;
873 }
874
875 kernel_fpu_begin();
876
877 /* calculate first value of T */
878 aesni_enc(aes_ctx(ctx->raw_tweak_ctx), walk.iv, walk.iv);
879
Leading to not entering this loop and so we don't restore kernel_fpu_end().
So maybe the "if (walk.nbytes == 0)" check should be moved to right
before the call to kernel_fpu_begin()?
880 while (walk.nbytes > 0) {
881 int nbytes = walk.nbytes;
882
883 if (nbytes < walk.total)
884 nbytes &= ~(AES_BLOCK_SIZE - 1);
885
886 if (encrypt)
887 aesni_xts_encrypt(aes_ctx(ctx->raw_crypt_ctx),
888 walk.dst.virt.addr, walk.src.virt.addr,
889 nbytes, walk.iv);
890 else
891 aesni_xts_decrypt(aes_ctx(ctx->raw_crypt_ctx),
892 walk.dst.virt.addr, walk.src.virt.addr,
893 nbytes, walk.iv);
894 kernel_fpu_end();
895
896 err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
897
898 if (walk.nbytes > 0)
899 kernel_fpu_begin();
900 }
901
902 if (unlikely(tail > 0 && !err)) {
903 struct scatterlist sg_src[2], sg_dst[2];
904 struct scatterlist *src, *dst;
905
906 dst = src = scatterwalk_ffwd(sg_src, req->src, req->cryptlen);
907 if (req->dst != req->src)
908 dst = scatterwalk_ffwd(sg_dst, req->dst, req->cryptlen);
909
910 skcipher_request_set_crypt(req, src, dst, AES_BLOCK_SIZE + tail,
911 req->iv);
912
913 err = skcipher_walk_virt(&walk, &subreq, false);
914 if (err)
--> 915 return err;
916
917 kernel_fpu_begin();
918 if (encrypt)
919 aesni_xts_encrypt(aes_ctx(ctx->raw_crypt_ctx),
920 walk.dst.virt.addr, walk.src.virt.addr,
921 walk.nbytes, walk.iv);
922 else
923 aesni_xts_decrypt(aes_ctx(ctx->raw_crypt_ctx),
924 walk.dst.virt.addr, walk.src.virt.addr,
925 walk.nbytes, walk.iv);
926 kernel_fpu_end();
927
928 err = skcipher_walk_done(&walk, 0);
929 }
930 return err;
931 }
regards,
dan carpenter
