Re: [PATCH v2] ARM: zImage: Fix stack overflow in merge_fdt_bootargs()

[Richard Genoud]

2017-07-22 15:02 GMT+02:00 Rask Ingemann Lambertsen <rask@xxxxxxxxxxxx>:
> This function is called very early on from head.S and currently sets up a
> stack frame of more than 1024 bytes:
>
> atags_to_fdt.c: In function âmerge_fdt_bootargsâ:
> atags_to_fdt.c:98:1: warning: the frame size of 1032 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>
> This causes a crash and failure to boot with some combinations of kernel
> version, gcc version and dtb, such as kernel version 4.1-rc1 or 4.1.0,
> gcc version 5.4.1 20161019 (Debian 5.4.1-3) and tegra20-trimslice.dtb.
>
> With this patch, merge_fdt_bootargs() is rewritten to not use a large buffer,
> thereby solving the problem of the stack overflow.
>
> As a side effect of this rewrite, you no longer get a space added in front
> of the kernel command line when no bootargs property was found in the FDT.
>
> Signed-off-by: Rask Ingemann Lambertsen <rask@xxxxxxxxxxxx>
> Tested-by: Pavel Machek <pavel@xxxxxx>
> Tested-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxxxx>
> Fixes: d0f34a11ddab ("ARM: 7437/1: zImage: Allow DTB command line concatenation with ATAG_CMDLINE")
seems good to me !
Reviewed-by: Richard Genoud <richard.genoud@xxxxxxxxx>

> ---
>
> I have tested that this works properly when
> a) only the FDT bootargs are provided,
> b) only the ATAG command line is provided, and
> c) both the FDT bootargs and the ATAG command line are provided.
>
> Changes from v1 to v2:
> The original "bootargs" NUL terminator is changed into a space only when
> appenprop_string() succeeds. Commented by Richard Genoud.
>
>  arch/arm/boot/compressed/atags_to_fdt.c | 59 +++++++++++++++++++++------------
>  1 file changed, 37 insertions(+), 22 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/atags_to_fdt.c b/arch/arm/boot/compressed/atags_to_fdt.c
> index 9448aa0c6686..87a5fba5a28e 100644
> --- a/arch/arm/boot/compressed/atags_to_fdt.c
> +++ b/arch/arm/boot/compressed/atags_to_fdt.c
> @@ -55,6 +55,29 @@ static const void *getprop(const void *fdt, const char *node_path,
>         return fdt_getprop(fdt, offset, property, len);
>  }
>
> +static int appendprop_string(void *fdt, const char *node_path,
> +                            const char *property, const char *string)
> +{
> +       int offset = node_offset(fdt, node_path);
> +
> +       if (offset < 0)
> +               return offset;
> +       return fdt_appendprop_string(fdt, offset, property, string);
> +}
> +
> +static int setprop_inplace_partial(void *fdt, const char *node_path,
> +                                  const char *property, unsigned int idx,
> +                                  const void *val, int len)
> +{
> +       int offset = node_offset(fdt, node_path);
> +
> +       if (offset < 0)
> +               return offset;
> +       return fdt_setprop_inplace_namelen_partial(fdt, offset, property,
> +                                                  strlen(property), idx,
> +                                                  val, len);
> +}
> +
>  static uint32_t get_cell_size(const void *fdt)
>  {
>         int len;
> @@ -66,35 +89,27 @@ static uint32_t get_cell_size(const void *fdt)
>         return cell_size;
>  }
>
> -static void merge_fdt_bootargs(void *fdt, const char *fdt_cmdline)
> -{
> -       char cmdline[COMMAND_LINE_SIZE];
> -       const char *fdt_bootargs;
> -       char *ptr = cmdline;
> -       int len = 0;
> -
> -       /* copy the fdt command line into the buffer */
> -       fdt_bootargs = getprop(fdt, "/chosen", "bootargs", &len);
> -       if (fdt_bootargs)
> -               if (len < COMMAND_LINE_SIZE) {
> -                       memcpy(ptr, fdt_bootargs, len);
> -                       /* len is the length of the string
> -                        * including the NULL terminator */
> -                       ptr += len - 1;
> -               }
> -
> -       /* and append the ATAG_CMDLINE */
> -       if (fdt_cmdline) {
> -               len = strlen(fdt_cmdline);
> -               if (ptr - cmdline + len + 2 < COMMAND_LINE_SIZE) {
> -                       *ptr++ = ' ';
> -                       memcpy(ptr, fdt_cmdline, len);
> -                       ptr += len;
> -               }
> -       }
> -       *ptr = '\0';
> -
> -       setprop_string(fdt, "/chosen", "bootargs", cmdline);
> +/* This is called early on from head.S, so it can't use much stack. */
> +static void merge_fdt_bootargs(void *fdt, const char *atag_cmdline)
> +{
> +       const char *fdt_bootargs;
> +       int len = 0;
> +
> +       /* With no ATAG command line or an empty one, there is nothing to do. */
> +       if (!atag_cmdline || strlen(atag_cmdline) == 0)
> +               return;
> +
> +       fdt_bootargs = getprop(fdt, "/chosen", "bootargs", &len);
> +
> +       /* With no FDT command line or an empty one, just use the ATAG one. */
> +       if (!fdt_bootargs || len <= 1) {
> +               setprop_string(fdt, "/chosen", "bootargs", atag_cmdline);
> +               return;
> +       }
> +       if (appendprop_string(fdt, "/chosen", "bootargs", atag_cmdline) < 0)
> +               return;
> +       /* Replace the previous NUL terminator with a space. */
> +       setprop_inplace_partial(fdt, "/chosen", "bootargs", len - 1, " ", 1);
>  }
>
>  /*
> --
> 2.13.2
>

Thanks !