linux-hardening - [PATCH][next] media: venus: hfi_cmds: Replace fake flex-array with flexible-array member

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Date:   Tue, 16 May 2023 19:03:39 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
        Vikash Garodia <quic_vgarodia@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] media: venus: hfi_cmds: Replace fake flex-array with
 flexible-array member

One-element arrays are deprecated, and we are replacing them with flexible
array members instead. So, replace one-element arrays with flexible-array
members in struct hfi_sys_set_resource_pkt, and refactor the rest of
the code, accordingly.

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [1].

The only binary differences seen before/after changes are the
following:

     17ba:      mov    %rbx,%rdi
     17bd:      call   17c2 <pkt_sys_set_resource+0x42>
                        17be: R_X86_64_PLT32    __tsan_write4-0x4
-    17c2:      movl   $0x14,(%rbx)
+    17c2:      movl   $0x10,(%rbx)
     17c8:      lea    0x4(%rbx),%rdi
     17cc:      call   17d1 <pkt_sys_set_resource+0x51>
                        17cd: R_X86_64_PLT32    __tsan_write4-0x4

which is expected once this accounts for the following line of code
at  drivers/media/platform/qcom/venus/hfi_cmds.c:73

73         pkt->hdr.size = sizeof(*pkt);

and as *pkt is of type struct hfi_sys_set_resource_pkt, sizeof(*pkt) is
reduced by 4 bytes, due to the flex-array transformation.

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/293
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 drivers/media/platform/qcom/venus/hfi_cmds.c | 2 +-
 drivers/media/platform/qcom/venus/hfi_cmds.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/platform/qcom/venus/hfi_cmds.c b/drivers/media/platform/qcom/venus/hfi_cmds.c
index 3f74d518ad08..7c82e212434e 100644
--- a/drivers/media/platform/qcom/venus/hfi_cmds.c
+++ b/drivers/media/platform/qcom/venus/hfi_cmds.c
@@ -83,7 +83,7 @@ int pkt_sys_set_resource(struct hfi_sys_set_resource_pkt *pkt, u32 id, u32 size,
 		res->size = size;
 		res->mem = addr;
 		pkt->resource_type = HFI_RESOURCE_OCMEM;
-		pkt->hdr.size += sizeof(*res) - sizeof(u32);
+		pkt->hdr.size += sizeof(*res);
 		break;
 	}
 	case VIDC_RESOURCE_NONE:
diff --git a/drivers/media/platform/qcom/venus/hfi_cmds.h b/drivers/media/platform/qcom/venus/hfi_cmds.h
index ba74d03eb9cd..dd9c5066442d 100644
--- a/drivers/media/platform/qcom/venus/hfi_cmds.h
+++ b/drivers/media/platform/qcom/venus/hfi_cmds.h
@@ -56,7 +56,7 @@ struct hfi_sys_set_resource_pkt {
 	struct hfi_pkt_hdr hdr;
 	u32 resource_handle;
 	u32 resource_type;
-	u32 resource_data[1];
+	u32 resource_data[];
 };
 
 struct hfi_sys_release_resource_pkt {
-- 
2.34.1