| Message ID | 20190519160446.320-2-hsinyi@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4,1/3] amr64: map FDT as RW for early_init_dt_scan() | expand |
On Mon, May 20, 2019 at 1:09 AM 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> > --- > change log v2->v4: > * v3 abandoned > * fix doc error > --- > Documentation/devicetree/bindings/chosen.txt | 14 ++++++++++++++ > drivers/of/fdt.c | 10 ++++++++++ > 2 files changed, 24 insertions(+) > > diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt > index 45e79172a646..678e81bc4383 100644 > --- a/Documentation/devicetree/bindings/chosen.txt > +++ b/Documentation/devicetree/bindings/chosen.txt > @@ -28,6 +28,20 @@ mode) when EFI_RNG_PROTOCOL is supported, it will be overwritten by > the Linux EFI stub (which will populate the property itself, using > EFI_RNG_PROTOCOL). > > +rng-seed > +----------- > + > +This property serves as an entropy to add device randomness. It is parsed > +as a byte array, e.g. > + > +/ { > + chosen { > + rng-seed = <0x31 0x95 0x1b 0x3c 0xc9 0xfa 0xb3 ...>; > + }; > +}; > + > +This random value should be provided by bootloader. > + > stdout-path > ----------- > > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c > index de893c9616a1..7f3d72921b23 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> Alphabetical order. > > #include <asm/setup.h> /* for COMMAND_LINE_SIZE */ > #include <asm/page.h> > @@ -1079,6 +1080,7 @@ 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); > > @@ -1113,6 +1115,14 @@ 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_delprop(initial_boot_params, node, "rng-seed"); I'm a little bit concerned about this, as we really want the rng-seed value to be wiped, and not kept in memory (even if it's hard to access). IIUC, fdt_delprop splices the device tree, so it'll override "rng-seed" property with whatever device tree entries follow it. However, if rng-seed is the last property (or if the entries that follow are smaller than rng-seed), the seed will stay in memory (or part of it). fdt_nop_property in v2 would erase it for sure. I don't know if there is a way to make sure that rng-seed is removed for good while still deleting the property (maybe modify fdt_splice_ to do a memset(.., 0) of the moved chunk?). > + } > + > /* break now */ > return 1; > } > -- > 2.20.1 >
On Mon, May 20, 2019 at 7:54 AM Nicolas Boichat <drinkcat@chromium.org> wrote: > Alphabetical order. Original headers are not sorted, should I sort them here? > > > I'm a little bit concerned about this, as we really want the rng-seed > value to be wiped, and not kept in memory (even if it's hard to > access). > > IIUC, fdt_delprop splices the device tree, so it'll override > "rng-seed" property with whatever device tree entries follow it. > However, if rng-seed is the last property (or if the entries that > follow are smaller than rng-seed), the seed will stay in memory (or > part of it). > > fdt_nop_property in v2 would erase it for sure. I don't know if there > is a way to make sure that rng-seed is removed for good while still > deleting the property (maybe modify fdt_splice_ to do a memset(.., 0) > of the moved chunk?). > So maybe we can use fdt_nop_property() back?
On Tue, May 21, 2019 at 12:10 PM Hsin-Yi Wang <hsinyi@chromium.org> wrote: > > On Mon, May 20, 2019 at 7:54 AM Nicolas Boichat <drinkcat@chromium.org> wrote: > > > Alphabetical order. > Original headers are not sorted, should I sort them here? > > > > > > > I'm a little bit concerned about this, as we really want the rng-seed > > value to be wiped, and not kept in memory (even if it's hard to > > access). > > > > IIUC, fdt_delprop splices the device tree, so it'll override > > "rng-seed" property with whatever device tree entries follow it. > > However, if rng-seed is the last property (or if the entries that > > follow are smaller than rng-seed), the seed will stay in memory (or > > part of it). > > > > fdt_nop_property in v2 would erase it for sure. I don't know if there > > is a way to make sure that rng-seed is removed for good while still > > deleting the property (maybe modify fdt_splice_ to do a memset(.., 0) > > of the moved chunk?). > > > So maybe we can use fdt_nop_property() back? Yes I prefer fdt_nop_property, if we don't want to modify delprop or splice. But it'd be good if others can chime in.
diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt index 45e79172a646..678e81bc4383 100644 --- a/Documentation/devicetree/bindings/chosen.txt +++ b/Documentation/devicetree/bindings/chosen.txt @@ -28,6 +28,20 @@ mode) when EFI_RNG_PROTOCOL is supported, it will be overwritten by the Linux EFI stub (which will populate the property itself, using EFI_RNG_PROTOCOL). +rng-seed +----------- + +This property serves as an entropy to add device randomness. It is parsed +as a byte array, e.g. + +/ { + chosen { + rng-seed = <0x31 0x95 0x1b 0x3c 0xc9 0xfa 0xb3 ...>; + }; +}; + +This random value should be provided by bootloader. + stdout-path ----------- diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c index de893c9616a1..7f3d72921b23 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> @@ -1079,6 +1080,7 @@ 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); @@ -1113,6 +1115,14 @@ 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_delprop(initial_boot_params, node, "rng-seed"); + } + /* break now */ return 1; }
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> --- change log v2->v4: * v3 abandoned * fix doc error --- Documentation/devicetree/bindings/chosen.txt | 14 ++++++++++++++ drivers/of/fdt.c | 10 ++++++++++ 2 files changed, 24 insertions(+)