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Limit output buffer size during decrypt fallback

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This is based on a patch submitted by Amlogic.

When we're doing decrypt fallback, either in the CDM or the OEMCrypto
tests, we sometimes fall back to a point where we're synthesizing new
samples and/or subsamples for the content being decrypted. When this
happens and the output buffer is clear, we should limit the size of the
output buffer to only the space needed to hold the output.

Previously, we've been passing the entire output buffer to every call.
This can create a problem if the reason for the fallback is a lack of
enough memory to communicate the buffers to the TA, since the output
buffer will remain the same size as the total output. Restricting the
buffer passed to each call to only the space needed by that call will
reduce the memory requirement.

Bug: 354834629
Test: x86-64
Merged from https://widevine-internal-review.googlesource.com/204810

Merged from https://widevine-internal-review.googlesource.com/204953

Change-Id: I412f43d8f88c72072ef1dd5293436bdb58e500b3
This commit is contained in:
John W. Bruce
2024-08-21 05:11:49 +00:00
parent 5a4a8fdede
commit a5bce8122e
2 changed files with 34 additions and 2 deletions
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16
libwvdrmengine/oemcrypto/test/oec_decrypt_fallback_chain.cpp
View File

@@ -17,7 +17,6 @@ void advance_dest_buffer(OEMCrypto_DestBufferDesc* dest_buffer, size_t bytes) {
switch (dest_buffer->type) {
case OEMCrypto_BufferType_Clear:
dest_buffer->buffer.clear.clear_buffer += bytes;
dest_buffer->buffer.clear.clear_buffer_length -= bytes;
break;
case OEMCrypto_BufferType_Secure:
@@ -99,6 +98,11 @@ OEMCryptoResult DecryptFallbackChain::DecryptSample(
const size_t length =
subsample.num_bytes_clear + subsample.num_bytes_encrypted;
fake_sample.buffers.input_data_length = length;
if (fake_sample.buffers.output_descriptor.type ==
OEMCrypto_BufferType_Clear) {
fake_sample.buffers.output_descriptor.buffer.clear.clear_buffer_length =
length;
}
fake_sample.subsamples = &subsample;
fake_sample.subsamples_length = 1;
@@ -144,6 +148,11 @@ OEMCryptoResult DecryptFallbackChain::DecryptSubsample(
if (subsample.num_bytes_clear > 0) {
fake_sample.buffers.input_data_length = subsample.num_bytes_clear;
if (fake_sample.buffers.output_descriptor.type ==
OEMCrypto_BufferType_Clear) {
fake_sample.buffers.output_descriptor.buffer.clear.clear_buffer_length =
subsample.num_bytes_clear;
}
fake_subsample.num_bytes_clear = subsample.num_bytes_clear;
fake_subsample.num_bytes_encrypted = 0;
fake_subsample.block_offset = 0;
@@ -167,6 +176,11 @@ OEMCryptoResult DecryptFallbackChain::DecryptSubsample(
if (subsample.num_bytes_encrypted > 0) {
fake_sample.buffers.input_data_length = subsample.num_bytes_encrypted;
if (fake_sample.buffers.output_descriptor.type ==
OEMCrypto_BufferType_Clear) {
fake_sample.buffers.output_descriptor.buffer.clear.clear_buffer_length =
subsample.num_bytes_encrypted;
}
fake_subsample.num_bytes_clear = 0;
fake_subsample.num_bytes_encrypted = subsample.num_bytes_encrypted;
fake_subsample.block_offset = subsample.block_offset;