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

[Klaus Jensen]

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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