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SubjectRe: [PATCH v2 1/3] KASLR: Parse all memmap entries in cmdline
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Hi Baoquan,

At 04/24/2017 10:40 AM, Baoquan He wrote:
> In commit:
>
> f28442497b5c ("x86/boot: Fix KASLR and memmap= collision")
>
> ... the memmap= option is parsed so that KASLR can avoid those reserved
> regions. It uses cmdline_find_option() to get the value if memmap=
> is specified, however the problem is that cmdline_find_option() can only
> find the last entry if multiple memmap entries are provided. This
> is not correct.
>
[...]
>
> -static void mem_avoid_memmap(void)
> +static void mem_avoid_memmap(char *str)
> {
> - char arg[128];
> int rc;
> - int i;
> - char *str;
> + int i = mem_avoid_memmap_index;

Is it better that we make that variable *static* to remove the global
variable(mem_avoid_memmap_index)?

- int i = mem_avoid_memmap_index;
+ static int i;

if (i >= MAX_MEMMAP_REGIONS)
return;
@@ -172,7 +172,6 @@ static void mem_avoid_memmap(char *str)
mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
i++;
}
- mem_avoid_memmap_index = i;

/* More than 4 memmaps, fail kaslr */
if ((i >= MAX_MEMMAP_REGIONS) && str)

>
> - /* See if we have any memmap areas */
> - rc = cmdline_find_option("memmap", arg, sizeof(arg));
> - if (rc <= 0)
> + if (i >= MAX_MEMMAP_REGIONS)
> return;
>

I guess we just parsed and handled 4 MEMMAP_REGIONS and might ignore
the following in the whole cmdline.

Is it reasonable? Is there any priority? The smaller the size, the more
priority?

Thanks,
Liyang

> - i = 0;
> - str = arg;
> while (str && (i < MAX_MEMMAP_REGIONS)) {
> int rc;
> unsigned long long start, size;
> @@ -196,12 +172,55 @@ static void mem_avoid_memmap(void)
> mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
> i++;
> }
> + mem_avoid_memmap_index = i;
>
> /* More than 4 memmaps, fail kaslr */
> if ((i >= MAX_MEMMAP_REGIONS) && str)
> memmap_too_large = true;
> }
>
> +
> +/* Macros used by the included decompressor code below. */
> +#define STATIC
> +#include <linux/decompress/mm.h>
> +
> +#define COMMAND_LINE_SIZE 256
> +static int handle_mem_memmap(void)
> +{
> + char *args = (char *)get_cmd_line_ptr();
> + size_t len = strlen((char *)args);
> + char *tmp_cmdline;
> + char *param, *val;
> +
> + tmp_cmdline = malloc(COMMAND_LINE_SIZE);
> + if (!tmp_cmdline )
> + error("Failed to allocate space for tmp_cmdline");
> +
> + len = (len >= COMMAND_LINE_SIZE) ? COMMAND_LINE_SIZE - 1 : len;
> + memcpy(tmp_cmdline, args, len);
> + tmp_cmdline[len] = 0;
> + args = tmp_cmdline;
> +
> + /* Chew leading spaces */
> + args = skip_spaces(args);
> +
> + while (*args) {
> + args = next_arg(args, &param, &val);
> + /* Stop at -- */
> + if (!val && strcmp(param, "--") == 0) {
> + warn("Only '--' specified in cmdline");
> + free(tmp_cmdline);
> + return -1;
> + }
> +
> + if (!strcmp(param, "memmap"))
> + mem_avoid_memmap(val);
> + }
> +
> + free(tmp_cmdline);
> + return 0;
> +}
> +
> /*
> * In theory, KASLR can put the kernel anywhere in the range of [16M, 64T).
> * The mem_avoid array is used to store the ranges that need to be avoided
> @@ -323,7 +342,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
> /* We don't need to set a mapping for setup_data. */
>
> /* Mark the memmap regions we need to avoid */
> - mem_avoid_memmap();
> + handle_mem_memmap();
>
> #ifdef CONFIG_X86_VERBOSE_BOOTUP
> /* Make sure video RAM can be used. */
> diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
> index 5457b02..630e366 100644
> --- a/arch/x86/boot/string.c
> +++ b/arch/x86/boot/string.c
> @@ -122,6 +122,14 @@ unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int bas
> return result;
> }
>
> +long simple_strtol(const char *cp, char **endp, unsigned int base)
> +{
> + if (*cp == '-')
> + return -simple_strtoull(cp + 1, endp, base);
> +
> + return simple_strtoull(cp, endp, base);
> +}
> +
> /**
> * strlen - Find the length of a string
> * @s: The string to be sized
>


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