Fix buffer overflow in volk_32fc_x2_square_dist_32f_a_sse3

[argilo]

When the vector length is less than 4, volk_32fc_x2_square_dist_32f_a_sse3 performs an out-of-bounds read. Its main loop is set up to fetch data one iteration ahead, but the edge case is not considered and the last iteration is executed unconditionally.

I tried removing the pre-fetch logic like in #565, but performance was reduced. So I added an if statement around the last iteration instead.

Valgrind report:

==649543== Invalid read of size 16
==649543==    at 0x4B371B1: _mm_load_ps (xmmintrin.h:927)
==649543==    by 0x4B371B1: volk_32fc_x2_square_dist_32f_a_sse3 (volk_32fc_x2_square_dist_32f.h:221)
==649543==    by 0x48D982F: volk_32fc_x2_square_dist_32f_manual (volk.c:9276)
==649543==    by 0x12ADE2: run_cast_test3(void (*)(void*, void*, void*, unsigned int, char const*), std::vector<void*, std::allocator<void*> >&, unsigned int, unsigned int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:279)
==649543==    by 0x128765: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, float, std::complex<float>, unsigned int, unsigned int, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, bool) (qa_utils.cc:672)
==649543==    by 0x127809: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, volk_test_params_t, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:507)
==649543==    by 0x11E0DD: main (volk_profile.cc:139)
==649543==  Address 0x5401d00 is 0 bytes after a block of size 32 alloc'd
==649543==    at 0x484E120: memalign (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==649543==    by 0x48BF2C9: volk_malloc (volk_malloc.c:71)
==649543==    by 0x12B2FA: volk_qa_aligned_mem_pool::get_new(unsigned long) (qa_utils.cc:484)
==649543==    by 0x127F8D: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, float, std::complex<float>, unsigned int, unsigned int, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, bool) (qa_utils.cc:602)
==649543==    by 0x127809: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, volk_test_params_t, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:507)
==649543==    by 0x11E0DD: main (volk_profile.cc:139)
==649543== 
==649543== Invalid read of size 4
==649543==    at 0x4B372AD: volk_32fc_x2_square_dist_32f_a_sse3 (volk_32fc_x2_square_dist_32f.h:236)
==649543==    by 0x48D982F: volk_32fc_x2_square_dist_32f_manual (volk.c:9276)
==649543==    by 0x12ADE2: run_cast_test3(void (*)(void*, void*, void*, unsigned int, char const*), std::vector<void*, std::allocator<void*> >&, unsigned int, unsigned int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:279)
==649543==    by 0x128765: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, float, std::complex<float>, unsigned int, unsigned int, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, bool) (qa_utils.cc:672)
==649543==    by 0x127809: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, volk_test_params_t, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:507)
==649543==    by 0x11E0DD: main (volk_profile.cc:139)
==649543==  Address 0x5401d10 is 16 bytes after a block of size 32 alloc'd
==649543==    at 0x484E120: memalign (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==649543==    by 0x48BF2C9: volk_malloc (volk_malloc.c:71)
==649543==    by 0x12B2FA: volk_qa_aligned_mem_pool::get_new(unsigned long) (qa_utils.cc:484)
==649543==    by 0x127F8D: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, float, std::complex<float>, unsigned int, unsigned int, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, bool) (qa_utils.cc:602)
==649543==    by 0x127809: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, volk_test_params_t, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:507)
==649543==    by 0x11E0DD: main (volk_profile.cc:139)
==649543== 
==649543== Invalid read of size 4
==649543==    at 0x4B372B8: volk_32fc_x2_square_dist_32f_a_sse3 (volk_32fc_x2_square_dist_32f.h:236)
==649543==    by 0x48D982F: volk_32fc_x2_square_dist_32f_manual (volk.c:9276)
==649543==    by 0x12ADE2: run_cast_test3(void (*)(void*, void*, void*, unsigned int, char const*), std::vector<void*, std::allocator<void*> >&, unsigned int, unsigned int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:279)
==649543==    by 0x128765: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, float, std::complex<float>, unsigned int, unsigned int, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, bool) (qa_utils.cc:672)
==649543==    by 0x127809: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, volk_test_params_t, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:507)
==649543==    by 0x11E0DD: main (volk_profile.cc:139)
==649543==  Address 0x5401d14 is 20 bytes after a block of size 32 alloc'd
==649543==    at 0x484E120: memalign (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==649543==    by 0x48BF2C9: volk_malloc (volk_malloc.c:71)
==649543==    by 0x12B2FA: volk_qa_aligned_mem_pool::get_new(unsigned long) (qa_utils.cc:484)
==649543==    by 0x127F8D: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, float, std::complex<float>, unsigned int, unsigned int, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, bool) (qa_utils.cc:602)
==649543==    by 0x127809: run_volk_tests(volk_func_desc, void (*)(), std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, volk_test_params_t, std::vector<volk_test_results_t, std::allocator<volk_test_results_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (qa_utils.cc:507)
==649543==    by 0x11E0DD: main (volk_profile.cc:139)
==649543== 

[jdemel]

LGTM.

This kernel is hard to read. These interleaved loads and stores are difficult to deal with.

Do you have benchmark numbers?

[argilo]

Actually it may have been poor benchmarking on my part (frequency scaling getting in the way). I tested with more iterations and under the same conditions, and removing the pre-fetch seems no worse. I've updated the PR accordingly.

[argilo]

Before:

RUN_VOLK_TESTS: volk_32fc_x2_square_dist_32f(131071,100000)
a_avx2 completed in 3308.81 ms
a_sse3 completed in 4039.83 ms
generic completed in 4848.9 ms
u_avx2 completed in 3495.01 ms

After:

RUN_VOLK_TESTS: volk_32fc_x2_square_dist_32f(131071,100000)
a_avx2 completed in 3314.61 ms
a_sse3 completed in 3996.41 ms
generic completed in 4825.26 ms
u_avx2 completed in 3359.85 ms

[argilo]

The test failures are unrelated; all due to #646.