Re: [PATCH 2/2] pstore-ram: Allow optional mapping with pgprot_noncached

From: Kees Cook
Date: Wed Dec 10 2014 - 16:16:29 EST

On Tue, Sep 16, 2014 at 1:50 PM, Tony Lindgren <tony@xxxxxxxxxxx> wrote:
> From: Tony Lindgren <tony@xxxxxxxxxxx>
> Date: Thu, 11 Sep 2014 15:02:37 -0700
> Subject: [PATCH] pstore-ram: Allow optional mapping with pgprot_noncached
>
> On some ARMs the memory can be mapped pgprot_noncached() and still
> be working for atomic operations. As pointed out by Colin Cross
> <ccross@xxxxxxxxxxx>, in some cases you do want to use
> pgprot_noncached() if the SoC supports it to see a debug printk
> just before a write hanging the system.
>
> On ARMs, the atomic operations on strongly ordered memory are
> implementation defined. So let's provide an optional kernel parameter
> for configuring pgprot_noncached(), and use pgprot_writecombine() by
> default.
>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Rob Herring <robherring2@xxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Anton Vorontsov <anton@xxxxxxxxxx>
> Cc: Colin Cross <ccross@xxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Olof Johansson <olof@xxxxxxxxx>
> Cc: Tony Luck <tony.luck@xxxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>

Sorry this got missed! I think rmk's concerns were addressed in this
v2. Tony (Luck), can you take this into your tree?

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks!

-Kees

>
> --- a/Documentation/ramoops.txt
> +++ b/Documentation/ramoops.txt
> @@ -14,11 +14,19 @@ survive after a restart.
>
> 1. Ramoops concepts
>
> -Ramoops uses a predefined memory area to store the dump. The start and size of
> -the memory area are set using two variables:
> +Ramoops uses a predefined memory area to store the dump. The start and size
> +and type of the memory area are set using three variables:
> * "mem_address" for the start
> * "mem_size" for the size. The memory size will be rounded down to a
> power of two.
> + * "mem_type" to specifiy if the memory type (default is pgprot_writecombine).
> +
> +Typically the default value of mem_type=0 should be used as that sets the pstore
> +mapping to pgprot_writecombine. Setting mem_type=1 attempts to use
> +pgprot_noncached, which only works on some platforms. This is because pstore
> +depends on atomic operations. At least on ARM, pgprot_noncached causes the
> +memory to be mapped strongly ordered, and atomic operations on strongly ordered
> +memory are implementation defined, and won't work on many ARMs such as omaps.
>
> The memory area is divided into "record_size" chunks (also rounded down to
> power of two) and each oops/panic writes a "record_size" chunk of
> @@ -55,6 +63,7 @@ Setting the ramoops parameters can be done in 2 different manners:
> static struct ramoops_platform_data ramoops_data = {
> .mem_size = <...>,
> .mem_address = <...>,
> + .mem_type = <...>,
> .record_size = <...>,
> .dump_oops = <...>,
> .ecc = <...>,
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -61,6 +61,11 @@ module_param(mem_size, ulong, 0400);
> MODULE_PARM_DESC(mem_size,
> "size of reserved RAM used to store oops/panic logs");
>
> +static unsigned int mem_type;
> +module_param(mem_type, uint, 0600);
> +MODULE_PARM_DESC(mem_type,
> + "set to 1 to try to use unbuffered memory (default 0)");
> +
> static int dump_oops = 1;
> module_param(dump_oops, int, 0600);
> MODULE_PARM_DESC(dump_oops,
> @@ -79,6 +84,7 @@ struct ramoops_context {
> struct persistent_ram_zone *fprz;
> phys_addr_t phys_addr;
> unsigned long size;
> + unsigned int memtype;
> size_t record_size;
> size_t console_size;
> size_t ftrace_size;
> @@ -358,7 +364,8 @@ static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
> size_t sz = cxt->record_size;
>
> cxt->przs[i] = persistent_ram_new(*paddr, sz, 0,
> - &cxt->ecc_info);
> + &cxt->ecc_info,
> + cxt->memtype);
> if (IS_ERR(cxt->przs[i])) {
> err = PTR_ERR(cxt->przs[i]);
> dev_err(dev, "failed to request mem region (0x%zx@0x%llx): %d\n",
> @@ -388,7 +395,7 @@ static int ramoops_init_prz(struct device *dev, struct ramoops_context *cxt,
> return -ENOMEM;
> }
>
> - *prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info);
> + *prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info, cxt->memtype);
> if (IS_ERR(*prz)) {
> int err = PTR_ERR(*prz);
>
> @@ -435,6 +442,7 @@ static int ramoops_probe(struct platform_device *pdev)
>
> cxt->size = pdata->mem_size;
> cxt->phys_addr = pdata->mem_address;
> + cxt->memtype = pdata->mem_type;
> cxt->record_size = pdata->record_size;
> cxt->console_size = pdata->console_size;
> cxt->ftrace_size = pdata->ftrace_size;
> @@ -564,6 +572,7 @@ static void ramoops_register_dummy(void)
>
> dummy_data->mem_size = mem_size;
> dummy_data->mem_address = mem_address;
> + dummy_data->mem_type = 0;
> dummy_data->record_size = record_size;
> dummy_data->console_size = ramoops_console_size;
> dummy_data->ftrace_size = ramoops_ftrace_size;
> --- a/fs/pstore/ram_core.c
> +++ b/fs/pstore/ram_core.c
> @@ -380,7 +380,8 @@ void persistent_ram_zap(struct persistent_ram_zone *prz)
> persistent_ram_update_header_ecc(prz);
> }
>
> -static void *persistent_ram_vmap(phys_addr_t start, size_t size)
> +static void *persistent_ram_vmap(phys_addr_t start, size_t size,
> + unsigned int memtype)
> {
> struct page **pages;
> phys_addr_t page_start;
> @@ -392,7 +393,10 @@ static void *persistent_ram_vmap(phys_addr_t start, size_t size)
> page_start = start - offset_in_page(start);
> page_count = DIV_ROUND_UP(size + offset_in_page(start), PAGE_SIZE);
>
> - prot = pgprot_writecombine(PAGE_KERNEL);
> + if (memtype)
> + prot = pgprot_noncached(PAGE_KERNEL);
> + else
> + prot = pgprot_writecombine(PAGE_KERNEL);
>
> pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
> if (!pages) {
> @@ -411,8 +415,11 @@ static void *persistent_ram_vmap(phys_addr_t start, size_t size)
> return vaddr;
> }
>
> -static void *persistent_ram_iomap(phys_addr_t start, size_t size)
> +static void *persistent_ram_iomap(phys_addr_t start, size_t size,
> + unsigned int memtype)
> {
> + void *va;
> +
> if (!request_mem_region(start, size, "persistent_ram")) {
> pr_err("request mem region (0x%llx@0x%llx) failed\n",
> (unsigned long long)size, (unsigned long long)start);
> @@ -422,19 +429,24 @@ static void *persistent_ram_iomap(phys_addr_t start, size_t size)
> buffer_start_add = buffer_start_add_locked;
> buffer_size_add = buffer_size_add_locked;
>
> - return ioremap_wc(start, size);
> + if (memtype)
> + va = ioremap(start, size);
> + else
> + va = ioremap_wc(start, size);
> +
> + return va;
> }
>
> static int persistent_ram_buffer_map(phys_addr_t start, phys_addr_t size,
> - struct persistent_ram_zone *prz)
> + struct persistent_ram_zone *prz, int memtype)
> {
> prz->paddr = start;
> prz->size = size;
>
> if (pfn_valid(start >> PAGE_SHIFT))
> - prz->vaddr = persistent_ram_vmap(start, size);
> + prz->vaddr = persistent_ram_vmap(start, size, memtype);
> else
> - prz->vaddr = persistent_ram_iomap(start, size);
> + prz->vaddr = persistent_ram_iomap(start, size, memtype);
>
> if (!prz->vaddr) {
> pr_err("%s: Failed to map 0x%llx pages at 0x%llx\n", __func__,
> @@ -500,7 +512,8 @@ void persistent_ram_free(struct persistent_ram_zone *prz)
> }
>
> struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
> - u32 sig, struct persistent_ram_ecc_info *ecc_info)
> + u32 sig, struct persistent_ram_ecc_info *ecc_info,
> + unsigned int memtype)
> {
> struct persistent_ram_zone *prz;
> int ret = -ENOMEM;
> @@ -511,7 +524,7 @@ struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
> goto err;
> }
>
> - ret = persistent_ram_buffer_map(start, size, prz);
> + ret = persistent_ram_buffer_map(start, size, prz, memtype);
> if (ret)
> goto err;
>
> --- a/include/linux/pstore_ram.h
> +++ b/include/linux/pstore_ram.h
> @@ -53,7 +53,8 @@ struct persistent_ram_zone {
> };
>
> struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
> - u32 sig, struct persistent_ram_ecc_info *ecc_info);
> + u32 sig, struct persistent_ram_ecc_info *ecc_info,
> + unsigned int memtype);
> void persistent_ram_free(struct persistent_ram_zone *prz);
> void persistent_ram_zap(struct persistent_ram_zone *prz);
>
> @@ -76,6 +77,7 @@ ssize_t persistent_ram_ecc_string(struct persistent_ram_zone *prz,
> struct ramoops_platform_data {
> unsigned long mem_size;
> unsigned long mem_address;
> + unsigned int mem_type;
> unsigned long record_size;
> unsigned long console_size;
> unsigned long ftrace_size;



--
Kees Cook
Chrome OS Security
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