Re: [PATCH 08/23] hw/block/nvme: Avoid dynamic stack allocation

[Klaus Jensen <its@irrelevant.dk>]

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On May  5 23:10, Philippe Mathieu-Daudé wrote:
>Use autofree heap allocation instead of variable-length
>array on the stack.
>
>Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>---
> hw/block/nvme.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
>diff --git a/hw/block/nvme.c b/hw/block/nvme.c
>index 2f6d4925826..905c4bb57af 100644
>--- a/hw/block/nvme.c
>+++ b/hw/block/nvme.c
>@@ -652,7 +652,7 @@ static uint16_t nvme_map_prp(NvmeCtrl *n, NvmeSg *sg, uint64_t prp1,
>     len -= trans_len;
>     if (len) {
>         if (len > n->page_size) {
>-            uint64_t prp_list[n->max_prp_ents];
>+            g_autofree uint64_t *prp_list = NULL;
>             uint32_t nents, prp_trans;
>             int i = 0;
>
>@@ -662,8 +662,10 @@ static uint16_t nvme_map_prp(NvmeCtrl *n, NvmeSg *sg, uint64_t prp1,
>              * that offset.
>              */
>             nents = (n->page_size - (prp2 & (n->page_size - 1))) >> 3;
>-            prp_trans = MIN(n->max_prp_ents, nents) * sizeof(uint64_t);
>-            ret = nvme_addr_read(n, prp2, (void *)prp_list, prp_trans);
>+            prp_trans = MIN(n->max_prp_ents, nents);
>+            prp_list = g_new(uint64_t, prp_trans);
>+            ret = nvme_addr_read(n, prp2, (void *)prp_list,
>+                                 prp_trans * sizeof(uint64_t));

prp_trans determines how much we must transfer, not the size of the 
prp_list. Subsequent PRP lists may contain more than nents PRPs, so this 
may now go out of bounds.

Just do the allocation when prp_list is declared:

     g_autofree uint64_t *prp_list = g_new(uint64_t, n->max_prp_ents);

>             if (ret) {
>                 trace_pci_nvme_err_addr_read(prp2);
>                 status = NVME_DATA_TRAS_ERROR;
>@@ -682,9 +684,8 @@ static uint16_t nvme_map_prp(NvmeCtrl *n, NvmeSg *sg, uint64_t prp1,
>                     i = 0;
>                     nents = (len + n->page_size - 1) >> n->page_bits;
>                     nents = MIN(nents, n->max_prp_ents);
>-                    prp_trans = nents * sizeof(uint64_t);
>                     ret = nvme_addr_read(n, prp_ent, (void *)prp_list,
>-                                         prp_trans);
>+                                         nents * sizeof(uint64_t));
>                     if (ret) {
>                         trace_pci_nvme_err_addr_read(prp_ent);
>                         status = NVME_DATA_TRAS_ERROR;
>@@ -2510,10 +2511,10 @@ static uint16_t nvme_dsm(NvmeCtrl *n, NvmeRequest *req)
>     if (attr & NVME_DSMGMT_AD) {
>         int64_t offset;
>         size_t len;
>-        NvmeDsmRange range[nr];
>+        g_autofree NvmeDsmRange *range = g_new(NvmeDsmRange, nr);
>         uintptr_t *discards = (uintptr_t *)&req->opaque;
>
>-        status = nvme_h2c(n, (uint8_t *)range, sizeof(range), req);
>+        status = nvme_h2c(n, (uint8_t *)range, sizeof(*range) * nr, req);
>         if (status) {
>             return status;
>         }

DSM change LGTM.

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