| Message ID | 20190612043258.166048-3-hsinyi@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | add support for rng-seed | expand |
On Tue, Jun 11, 2019 at 10:34 PM Hsin-Yi Wang <hsinyi@chromium.org> wrote: > > Introducing a chosen node, rng-seed, which is an entropy that can be > passed to kernel called very early to increase initial device > randomness. Bootloader should provide this entropy and the value is > read from /chosen/rng-seed in DT. > > Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org> > Reviewed-by: Stephen Boyd <swboyd@chromium.org> > --- > change log v5->v6: > * remove Documentation change > --- > drivers/of/fdt.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) I assume this will go thru the arm64 tree. Reviewed-by: Rob Herring <robh@kernel.org>
On Wed, Jun 12, 2019 at 12:33:00PM +0800, Hsin-Yi Wang wrote: > Introducing a chosen node, rng-seed, which is an entropy that can be > passed to kernel called very early to increase initial device > randomness. Bootloader should provide this entropy and the value is > read from /chosen/rng-seed in DT. Could you please elaborate on this? * What is this initial entropy used by, and why is this important? I assume that devices which can populate this will have a HW RNG that the kernel will eventually make use of. * How much entropy is necessary or sufficient? * Why is the DT the right mechanism for this? Thanks, Mark. > > Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org> > Reviewed-by: Stephen Boyd <swboyd@chromium.org> > --- > change log v5->v6: > * remove Documentation change > --- > drivers/of/fdt.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c > index 3d36b5afd9bd..369130dbd42c 100644 > --- a/drivers/of/fdt.c > +++ b/drivers/of/fdt.c > @@ -24,6 +24,7 @@ > #include <linux/debugfs.h> > #include <linux/serial_core.h> > #include <linux/sysfs.h> > +#include <linux/random.h> > > #include <asm/setup.h> /* for COMMAND_LINE_SIZE */ > #include <asm/page.h> > @@ -1052,6 +1053,7 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, > { > int l; > const char *p; > + const void *rng_seed; > > pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname); > > @@ -1086,6 +1088,14 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, > > pr_debug("Command line is: %s\n", (char*)data); > > + rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l); > + if (rng_seed && l > 0) { > + add_device_randomness(rng_seed, l); > + > + /* try to clear seed so it won't be found. */ > + fdt_nop_property(initial_boot_params, node, "rng-seed"); > + } > + > /* break now */ > return 1; > } > -- > 2.20.1 >
On Fri, Jun 28, 2019 at 5:35 PM Mark Rutland <mark.rutland@arm.com> wrote: > > On Wed, Jun 12, 2019 at 12:33:00PM +0800, Hsin-Yi Wang wrote: > > Introducing a chosen node, rng-seed, which is an entropy that can be > > passed to kernel called very early to increase initial device > > randomness. Bootloader should provide this entropy and the value is > > read from /chosen/rng-seed in DT. > > Could you please elaborate on this? > > * What is this initial entropy used by, and why is this important? I > assume that devices which can populate this will have a HW RNG that > the kernel will eventually make use of. There are a few discussions here[0]. We basically want to add more randomness for stack canary when device just boot and not much device randomness was added. [0] https://lore.kernel.org/patchwork/patch/1070974/#1268553 On Thu, May 9, 2019 at 1:00 AM Hsin-Yi Wang <hsinyi@chromium.org> wrote: > This early added entropy is also going to be used for stack canary. At > the time it's created there's not be much entropy (before > boot_init_stack_canary(), there's only add_latent_entropy() and > command_line). > On arm64, there is a single canary for all tasks. If RNG is weak or > the seed can be read, it might be easier to figure out the canary. With newer compilers[1] there will be a per-task canary on arm64[2], which will improve this situation, but many architectures lack a per-task canary, unfortunately. I've also recently rearranged the RNG initialization[3] which should also help with better entropy mixing. But each of these are kind of band-aids against not having sufficient initial entropy, which leaves the canary potentially exposed. -Kees [1] https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=359c1bf35e3109d2f3882980b47a5eae46123259 [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0a1213fa7432778b71a1c0166bf56660a3aab030 [3] https://git.kernel.org/pub/scm/linux/kernel/git/tytso/random.git/commit/?h=dev&id=d55535232c3dbde9a523a9d10d68670f5fe5dec3 > > * How much entropy is necessary or sufficient? 64 bytes should be enough. But depends on how much bootloader can provide. > > * Why is the DT the right mechanism for this? EFI based systems can inject randomness in early boot. This is aimed to support DT based systems to also have this feature. https://github.com/torvalds/linux/commit/636259880a7e7d3446a707dddebc799da94bdd0b#diff-3ded2fe21b37c6f3e86c2a8418507714 Thanks
diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c index 3d36b5afd9bd..369130dbd42c 100644 --- a/drivers/of/fdt.c +++ b/drivers/of/fdt.c @@ -24,6 +24,7 @@ #include <linux/debugfs.h> #include <linux/serial_core.h> #include <linux/sysfs.h> +#include <linux/random.h> #include <asm/setup.h> /* for COMMAND_LINE_SIZE */ #include <asm/page.h> @@ -1052,6 +1053,7 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, { int l; const char *p; + const void *rng_seed; pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname); @@ -1086,6 +1088,14 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, pr_debug("Command line is: %s\n", (char*)data); + rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l); + if (rng_seed && l > 0) { + add_device_randomness(rng_seed, l); + + /* try to clear seed so it won't be found. */ + fdt_nop_property(initial_boot_params, node, "rng-seed"); + } + /* break now */ return 1; }