| Message ID | 20220607111514.755009-1-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | random: defer use of bootloader randomness to random_init() | expand |
Yet another approach would be to mix immediately, but defer crediting until random_init(). Jason
Hi Jason, On Tue, 7 Jun 2022 at 13:15, Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > Stephen reported that a static key warning splat appears during early > boot on systems that credit randomness from device trees that contain an > "rng-seed" property, because because setup_machine_fdt() is called > before jump_label_init() during setup_arch(): > > static_key_enable_cpuslocked(): static key '0xffffffe51c6fcfc0' used before call to jump_label_init() > WARNING: CPU: 0 PID: 0 at kernel/jump_label.c:166 static_key_enable_cpuslocked+0xb0/0xb8 > Modules linked in: > CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0+ #224 44b43e377bfc84bc99bb5ab885ff694984ee09ff > pstate: 600001c9 (nZCv dAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--) > pc : static_key_enable_cpuslocked+0xb0/0xb8 > lr : static_key_enable_cpuslocked+0xb0/0xb8 > sp : ffffffe51c393cf0 > x29: ffffffe51c393cf0 x28: 000000008185054c x27: 00000000f1042f10 > x26: 0000000000000000 x25: 00000000f10302b2 x24: 0000002513200000 > x23: 0000002513200000 x22: ffffffe51c1c9000 x21: fffffffdfdc00000 > x20: ffffffe51c2f0831 x19: ffffffe51c6fcfc0 x18: 00000000ffff1020 > x17: 00000000e1e2ac90 x16: 00000000000000e0 x15: ffffffe51b710708 > x14: 0000000000000066 x13: 0000000000000018 x12: 0000000000000000 > x11: 0000000000000000 x10: 00000000ffffffff x9 : 0000000000000000 > x8 : 0000000000000000 x7 : 61632065726f6665 x6 : 6220646573752027 > x5 : ffffffe51c641d25 x4 : ffffffe51c13142c x3 : ffff0a00ffffff05 > x2 : 40000000ffffe003 x1 : 00000000000001c0 x0 : 0000000000000065 > Call trace: > static_key_enable_cpuslocked+0xb0/0xb8 > static_key_enable+0x2c/0x40 > crng_set_ready+0x24/0x30 > execute_in_process_context+0x80/0x90 > _credit_init_bits+0x100/0x154 > add_bootloader_randomness+0x64/0x78 > early_init_dt_scan_chosen+0x140/0x184 > early_init_dt_scan_nodes+0x28/0x4c > early_init_dt_scan+0x40/0x44 > setup_machine_fdt+0x7c/0x120 > setup_arch+0x74/0x1d8 > start_kernel+0x84/0x44c > __primary_switched+0xc0/0xc8 > ---[ end trace 0000000000000000 ]--- > random: crng init done > Machine model: Google Lazor (rev1 - 2) with LTE > > A trivial fix went in to address this on arm64, 73e2d827a501 ("arm64: > Initialize jump labels before setup_machine_fdt()"). But it appears that > fixing it on other platforms might not be so trivial. And in the past > there have been problems related to add_bootloader_randomness() being > called too early in boot for what it needed. > > This patch defers all entropy crediting until random_init(), where we > can be sure that all facilities we need are up and running. It changes > the name add_bootloader_randomness() to register_bootloader_seed(), and > insists that its buffer remain alive during all of __init. > > A potential downside is that EFI runs a little bit before random_init(), > which means we were getting that seed a lot earlier before. > > Fixes: f5bda35fba61 ("random: use static branch for crng_ready()") > Reported-by: Stephen Boyd <swboyd@chromium.org> > Cc: Ard Biesheuvel <ardb@kernel.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Russell King <linux@armlinux.org.uk> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Phil Elwell <phil@raspberrypi.com> > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > --- > Ard - I guess we've got two things to figure out here: > > 1) How much we gain by the situation before this patch of EFI supplying > its seed before random_init(). > 2) Whether those buffers are guaranteed to live throughout __init, or if > this patch introduces a UaF. > This is not going to work, I'm afraid - please see below. > drivers/char/random.c | 38 ++++++++++++++++++-------------------- > drivers/firmware/efi/efi.c | 2 +- > drivers/of/fdt.c | 2 +- > include/linux/random.h | 2 +- > 4 files changed, 21 insertions(+), 23 deletions(-) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 4862d4d3ec49..d9d00143c7c5 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -678,7 +678,6 @@ static void __cold _credit_init_bits(size_t bits) > * > * void add_device_randomness(const void *buf, size_t len); > * void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy); > - * void add_bootloader_randomness(const void *buf, size_t len); > * void add_vmfork_randomness(const void *unique_vm_id, size_t len); > * void add_interrupt_randomness(int irq); > * void add_input_randomness(unsigned int type, unsigned int code, unsigned int value); > @@ -696,10 +695,6 @@ static void __cold _credit_init_bits(size_t bits) > * entropy as specified by the caller. If the entropy pool is full it will > * block until more entropy is needed. > * > - * add_bootloader_randomness() is called by bootloader drivers, such as EFI > - * and device tree, and credits its input depending on whether or not the > - * configuration option CONFIG_RANDOM_TRUST_BOOTLOADER is set. > - * > * add_vmfork_randomness() adds a unique (but not necessarily secret) ID > * representing the current instance of a VM to the pool, without crediting, > * and then force-reseeds the crng so that it takes effect immediately. > @@ -765,6 +760,18 @@ static int random_pm_notification(struct notifier_block *nb, unsigned long actio > > static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification }; > > +/* > + * Handle random seed passed by bootloader. The buf pointer > + * must remain alive during the kernel's init sequence. > + */ > +static __initdata const void *bootloader_seed; > +static __initdata size_t bootloader_seed_bytes; > +void __init register_bootloader_seed(const void *buf, size_t len) > +{ > + bootloader_seed = buf; > + bootloader_seed_bytes = len; > +} > + > /* > * The first collection of entropy occurs at system boot while interrupts > * are still turned off. Here we push in latent entropy, RDSEED, a timestamp, > @@ -793,6 +800,8 @@ int __init random_init(const char *command_line) > } > _mix_pool_bytes(&entropy, sizeof(entropy)); > } > + if (bootloader_seed && bootloader_seed_bytes) > + _mix_pool_bytes(bootloader_seed, bootloader_seed_bytes); > _mix_pool_bytes(&now, sizeof(now)); > _mix_pool_bytes(utsname(), sizeof(*(utsname()))); > _mix_pool_bytes(command_line, strlen(command_line)); > @@ -800,9 +809,10 @@ int __init random_init(const char *command_line) > > if (crng_ready()) > crng_reseed(); > - else if (trust_cpu) > - _credit_init_bits(arch_bytes * 8); > - used_arch_random = arch_bytes * 8 >= POOL_READY_BITS; > + else > + _credit_init_bits((trust_cpu ? arch_bytes * 8 : 0) + > + (trust_bootloader ? bootloader_seed_bytes * 8 : 0)); > + used_arch_random = arch_bytes * 8 + bootloader_seed_bytes * 8 >= POOL_READY_BITS; > > WARN_ON(register_pm_notifier(&pm_notifier)); > > @@ -861,18 +871,6 @@ void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy) > } > EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); > > -/* > - * Handle random seed passed by bootloader, and credit it if > - * CONFIG_RANDOM_TRUST_BOOTLOADER is set. > - */ > -void __cold add_bootloader_randomness(const void *buf, size_t len) > -{ > - mix_pool_bytes(buf, len); > - if (trust_bootloader) > - credit_init_bits(len * 8); > -} > -EXPORT_SYMBOL_GPL(add_bootloader_randomness); > - > #if IS_ENABLED(CONFIG_VMGENID) > static BLOCKING_NOTIFIER_HEAD(vmfork_chain); > > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c > index 860534bcfdac..daf374983012 100644 > --- a/drivers/firmware/efi/efi.c > +++ b/drivers/firmware/efi/efi.c > @@ -614,7 +614,7 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables, > sizeof(*seed) + size); > if (seed != NULL) { > pr_notice("seeding entropy pool\n"); > - add_bootloader_randomness(seed->bits, size); > + register_bootloader_seed(seed->bits, size); The next line says it all, really: the seed is in a firmware table somewhere, and only gets mapped temporarily here. Note that we cannot copy it either, as we are running way before we have discovered where RAM is to begin with. > early_memunmap(seed, sizeof(*seed) + size); > } else { > pr_err("Could not map UEFI random seed!\n"); > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c > index a8f5b6532165..389ef0f781c2 100644 > --- a/drivers/of/fdt.c > +++ b/drivers/of/fdt.c > @@ -1201,7 +1201,7 @@ int __init early_init_dt_scan_chosen(char *cmdline) > > rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l); > if (rng_seed && l > 0) { > - add_bootloader_randomness(rng_seed, l); > + register_bootloader_seed(rng_seed, l); > > /* try to clear seed so it won't be found. */ > fdt_nop_property(initial_boot_params, node, "rng-seed"); > diff --git a/include/linux/random.h b/include/linux/random.h > index fae0c84027fd..c4fa7ca008df 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -13,7 +13,6 @@ > struct notifier_block; > > void add_device_randomness(const void *buf, size_t len); > -void add_bootloader_randomness(const void *buf, size_t len); > void add_input_randomness(unsigned int type, unsigned int code, > unsigned int value) __latent_entropy; > void add_interrupt_randomness(int irq) __latent_entropy; > @@ -72,6 +71,7 @@ static inline unsigned long get_random_canary(void) > return get_random_long() & CANARY_MASK; > } > > +void __init register_bootloader_seed(const void *buf, size_t len); > int __init random_init(const char *command_line); > bool rng_is_initialized(void); > bool rng_has_arch_random(void); More fundamentally, I feel we are losing sight of the actual issue. This is another patch that makes potentially risky functional changes to very early boot code, only so that we can manipulate the static key as early as we think we need to. So could we please go back to some basic questions here; - Why do we need/want a static key here to begin with? Is is for performance? - Why do we need to enable this static key so early? - Even if very convincing replies can be given to the previous two points, wouldn't it be betterr to simply revert the -stable backport that introduces the use of the static key, and find a robust and portable solution for after v5.19?
Hi Ard, On Tue, Jun 07, 2022 at 01:55:37PM +0200, Ard Biesheuvel wrote: > This is not going to work, I'm afraid - please see below. > > The next line says it all, really: the seed is in a firmware table > somewhere, and only gets mapped temporarily here. Note that we cannot > copy it either, as we are running way before we have discovered where > RAM is to begin with. Oh, darn. Okay. The v2 might be a bit more palpable then. It mixes immediately, but defers crediting: [1] https://lore.kernel.org/lkml/20220607113238.769088-1-Jason@zx2c4.com/ > - Even if very convincing replies can be given to the previous two > points, wouldn't it be betterr to simply revert the -stable backport > that introduces the use of the static key, and find a robust and > portable solution for after v5.19? This has already been done: [2] https://lore.kernel.org/stable/20220607084005.666059-1-Jason@zx2c4.com/ And mentioned here: [3] https://lore.kernel.org/lkml/CAHmME9rJif3ydZuFJcSjPxkGMofZkbu2PXcHBF23OWVgGQ4c+A@mail.gmail.com/ You're on this thread. > So could we please go back to some basic questions here; > - Why do we need/want a static key here to begin with? Is is for performance? > - Why do we need to enable this static key so early? We don't need to enable it especially early. I've now sent three different approaches for deferring it until later and you suggested one. The first of mine is kind of ugly (checking static_key_initialized and such at different points). Your suggested one after that did the same but deferred into crng_reseed(), which I'm not a fan of. My second one is this patch, which is flawed for the reason you pointed out. But perhaps my third one is the right amount of simple and okay? That's the one I linked up top, [1]. Let me know what you think of that. My motivation for not wanting to defer it is that if the arch solution winds up being easy and straight forward (as it was for arm64), then it would be nice to not need to clutter up random.c as a result. But if the arch solution winds up looking fragile or problematic somehow, then one of these solutions should do the trick. In particular [1] seems nice enough that it doesn't really even clutter things up too much as feared. Jason
On Tue, 7 Jun 2022 at 14:05, Jason A. Donenfeld <Jason@zx2c4.com> wrote: > On Tue, Jun 07, 2022 at 01:55:37PM +0200, Ard Biesheuvel wrote: > > This is not going to work, I'm afraid - please see below. > > > > The next line says it all, really: the seed is in a firmware table > > somewhere, and only gets mapped temporarily here. Note that we cannot > > copy it either, as we are running way before we have discovered where > > RAM is to begin with. > > Oh, darn. Okay. The v2 might be a bit more palpable then. It mixes > immediately, but defers crediting: > > [1] https://lore.kernel.org/lkml/20220607113238.769088-1-Jason@zx2c4.com/ > > > - Even if very convincing replies can be given to the previous two > > points, wouldn't it be betterr to simply revert the -stable backport > > that introduces the use of the static key, and find a robust and > > portable solution for after v5.19? > > This has already been done: > > [2] https://lore.kernel.org/stable/20220607084005.666059-1-Jason@zx2c4.com/ > > And mentioned here: > > [3] https://lore.kernel.org/lkml/CAHmME9rJif3ydZuFJcSjPxkGMofZkbu2PXcHBF23OWVgGQ4c+A@mail.gmail.com/ > > You're on this thread. > OK, excellent, thanks for confirming. There are so many threads now going on at the same time that I lost track. > > So could we please go back to some basic questions here; > > - Why do we need/want a static key here to begin with? Is is for performance? You still haven't answered this question, f5bda35fba61 only reasons about how we can use a static branch but not why we should. Note that jump labels use asm() blocks, which are opaque to the compiler, and so it is not guaranteed that codegen will be better than a single conditional branch that will always be predicted correctly at runtime. And it clutters up the code, given that you need to use the execute_in_process_context() helper to perform the static key manipulation outside of the calling context. > > - Why do we need to enable this static key so early? > > We don't need to enable it especially early. I've now sent three > different approaches for deferring it until later and you suggested one. > The first of mine is kind of ugly (checking static_key_initialized and > such at different points). Your suggested one after that did the same > but deferred into crng_reseed(), which I'm not a fan of. My second one > is this patch, which is flawed for the reason you pointed out. But > perhaps my third one is the right amount of simple and okay? That's the > one I linked up top, [1]. Let me know what you think of that. > > My motivation for not wanting to defer it is that if the arch solution > winds up being easy and straight forward (as it was for arm64), then it > would be nice to not need to clutter up random.c as a result. If clutter is a concern, how about getting rid of the execute_in_process_context() dance, and just use a late_initcall() instead? > But if > the arch solution winds up looking fragile or problematic somehow, then > one of these solutions should do the trick. In particular [1] seems nice > enough that it doesn't really even clutter things up too much as feared. > As I replied there, I think that patch is not as bad as the other ones that have been suggested (including mine). But I still feel we are going through a lot of trouble to enable something that we really don't need here.
Hi Ard, On Tue, Jun 07, 2022 at 02:15:27PM +0200, Ard Biesheuvel wrote: > Note that jump labels use asm() blocks, which are opaque to the > compiler, and so it is not guaranteed that codegen will be better than I actually spent a lot of time looking at the codegen on a few platforms. > > > - Why do we need to enable this static key so early? > > > > We don't need to enable it especially early. I've now sent three > > different approaches for deferring it until later and you suggested one. > > The first of mine is kind of ugly (checking static_key_initialized and > > such at different points). Your suggested one after that did the same > > but deferred into crng_reseed(), which I'm not a fan of. My second one > > is this patch, which is flawed for the reason you pointed out. But > > perhaps my third one is the right amount of simple and okay? That's the > > one I linked up top, [1]. Let me know what you think of that. > > > > My motivation for not wanting to defer it is that if the arch solution > > winds up being easy and straight forward (as it was for arm64), then it > > would be nice to not need to clutter up random.c as a result. > > If clutter is a concern, how about getting rid of the > execute_in_process_context() dance, and just use a late_initcall() > instead? As I already explained in [1], this does not work. If the order is (A)(B), then all this will happen *after* the late init call. [1] https://lore.kernel.org/lkml/Yp8oOH+9V336LrLk@zx2c4.com/ Jason
On Tue, 7 Jun 2022 at 14:22, Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > Hi Ard, > > On Tue, Jun 07, 2022 at 02:15:27PM +0200, Ard Biesheuvel wrote: > > Note that jump labels use asm() blocks, which are opaque to the > > compiler, and so it is not guaranteed that codegen will be better than > > I actually spent a lot of time looking at the codegen on a few > platforms. > I did a quick experiment on ThunderX2 with the following program #include <stdio.h> #include <stdlib.h> #include <sys/random.h> static unsigned char buf[16]; int main(void) { for (int i = 0; i < 1000000; i++) { if (getrandom(buf, sizeof(buf), GRND_RANDOM | GRND_NONBLOCK) < sizeof(buf)) { fprintf(stderr, "getrandom() error!\n"); exit(-1); } } return 0; } both with and without your revert patch of f5bda35fba615ac applied onto v5.19-rc1, the results are below (Cortex-A57 @ 2 GHz): ############## WITH STATIC BRANCH ard@dogfood:~$ perf_5.10 stat ./rnd Performance counter stats for './rnd': 906.01 msec task-clock # 0.999 CPUs utilized 2 context-switches # 0.002 K/sec 0 cpu-migrations # 0.000 K/sec 40 page-faults # 0.044 K/sec 1,812,010,034 cycles # 2.000 GHz 1,944,549,733 instructions # 1.07 insn per cycle <not supported> branches 2,014,408 branch-misses 0.906695576 seconds time elapsed 0.140334000 seconds user 0.765871000 seconds sys ard@dogfood:~$ perf_5.10 stat ./rnd Performance counter stats for './rnd': 918.37 msec task-clock # 0.999 CPUs utilized 2 context-switches # 0.002 K/sec 0 cpu-migrations # 0.000 K/sec 37 page-faults # 0.040 K/sec 1,836,733,451 cycles # 2.000 GHz 1,944,572,442 instructions # 1.06 insn per cycle <not supported> branches 3,012,020 branch-misses 0.919027080 seconds time elapsed 0.159721000 seconds user 0.758718000 seconds sys ard@dogfood:~$ perf_5.10 stat ./rnd Performance counter stats for './rnd': 902.06 msec task-clock # 0.999 CPUs utilized 1 context-switches # 0.001 K/sec 0 cpu-migrations # 0.000 K/sec 39 page-faults # 0.043 K/sec 1,804,103,600 cycles # 2.000 GHz 1,944,563,889 instructions # 1.08 insn per cycle <not supported> branches 1,956,027 branch-misses 0.902793520 seconds time elapsed 0.172464000 seconds user 0.729822000 seconds sys ############## WITHOUT STATIC BRANCH ard@dogfood:~$ perf_5.10 stat ./rnd Performance counter stats for './rnd': 924.79 msec task-clock # 0.999 CPUs utilized 2 context-switches # 0.002 K/sec 0 cpu-migrations # 0.000 K/sec 39 page-faults # 0.042 K/sec 1,849,568,681 cycles # 2.000 GHz 1,950,584,115 instructions # 1.05 insn per cycle <not supported> branches 4,012,227 branch-misses 0.925500832 seconds time elapsed 0.204227000 seconds user 0.720739000 seconds sys ard@dogfood:~$ perf_5.10 stat ./rnd Performance counter stats for './rnd': 933.06 msec task-clock # 0.999 CPUs utilized 2 context-switches # 0.002 K/sec 0 cpu-migrations # 0.000 K/sec 39 page-faults # 0.042 K/sec 1,866,097,571 cycles # 2.000 GHz 1,950,574,944 instructions # 1.05 insn per cycle <not supported> branches 3,984,008 branch-misses 0.933798032 seconds time elapsed 0.323067000 seconds user 0.610271000 seconds sys ard@dogfood:~$ perf_5.10 stat ./rnd Performance counter stats for './rnd': 913.16 msec task-clock # 0.999 CPUs utilized 1 context-switches # 0.001 K/sec 0 cpu-migrations # 0.000 K/sec 37 page-faults # 0.041 K/sec 1,826,308,530 cycles # 2.000 GHz 1,950,559,902 instructions # 1.07 insn per cycle <not supported> branches 2,231,050 branch-misses 0.913874672 seconds time elapsed 0.164228000 seconds user 0.749157000 seconds sys So that's a 0.3% reduction (in terms of actual instructions executed) in a synthetic benchmark that does nothing but call getrandom() in a tight loop. In other words, I think the static branch solves a problem that does not exist. > > > > - Why do we need to enable this static key so early? > > > > > > We don't need to enable it especially early. I've now sent three > > > different approaches for deferring it until later and you suggested one. > > > The first of mine is kind of ugly (checking static_key_initialized and > > > such at different points). Your suggested one after that did the same > > > but deferred into crng_reseed(), which I'm not a fan of. My second one > > > is this patch, which is flawed for the reason you pointed out. But > > > perhaps my third one is the right amount of simple and okay? That's the > > > one I linked up top, [1]. Let me know what you think of that. > > > > > > My motivation for not wanting to defer it is that if the arch solution > > > winds up being easy and straight forward (as it was for arm64), then it > > > would be nice to not need to clutter up random.c as a result. > > > > If clutter is a concern, how about getting rid of the > > execute_in_process_context() dance, and just use a late_initcall() > > instead? > > As I already explained in [1], this does not work. If the order is > (A)(B), then all this will happen *after* the late init call. > > [1] https://lore.kernel.org/lkml/Yp8oOH+9V336LrLk@zx2c4.com/ > Yeah, I guess finding the right spot is tricky. The more reason just to drop it altogether.
Hi Ard, On Tue, Jun 07, 2022 at 04:19:26PM +0200, Ard Biesheuvel wrote: > #include <stdio.h> > #include <stdlib.h> > #include <sys/random.h> > > static unsigned char buf[16]; > > int main(void) > { > for (int i = 0; i < 1000000; i++) { > if (getrandom(buf, sizeof(buf), > GRND_RANDOM | GRND_NONBLOCK) < sizeof(buf)) { > fprintf(stderr, "getrandom() error!\n"); > exit(-1); > } > } > return 0; > } I'm actually more worried about the random input flow than the random output flow and branch misprediction. But more generally, I'd just like to keep that code as cold as possible after crng init. It's code that's only used in that one phase and then never again. It can be entirely disabled. Anyway, we've got a few solutions now to pick from on the random.c side of things. I'm going to investigate the arm32 situation next. And then we'll see what it all looks like. Jason
On Tue, 7 Jun 2022 at 16:48, Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > Hi Ard, > > On Tue, Jun 07, 2022 at 04:19:26PM +0200, Ard Biesheuvel wrote: > > #include <stdio.h> > > #include <stdlib.h> > > #include <sys/random.h> > > > > static unsigned char buf[16]; > > > > int main(void) > > { > > for (int i = 0; i < 1000000; i++) { > > if (getrandom(buf, sizeof(buf), > > GRND_RANDOM | GRND_NONBLOCK) < sizeof(buf)) { > > fprintf(stderr, "getrandom() error!\n"); > > exit(-1); > > } > > } > > return 0; > > } > > I'm actually more worried about the random input flow than the random > output flow and branch misprediction. But more generally, I'd just like > to keep that code as cold as possible after crng init. It's code that's > only used in that one phase and then never again. It can be entirely > disabled. > > Anyway, we've got a few solutions now to pick from on the random.c side > of things. I'm going to investigate the arm32 situation next. And then > we'll see what it all looks like. > Sure. It would be helpful if some other folks could chime in as well?
diff --git a/drivers/char/random.c b/drivers/char/random.c index 4862d4d3ec49..d9d00143c7c5 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -678,7 +678,6 @@ static void __cold _credit_init_bits(size_t bits) * * void add_device_randomness(const void *buf, size_t len); * void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy); - * void add_bootloader_randomness(const void *buf, size_t len); * void add_vmfork_randomness(const void *unique_vm_id, size_t len); * void add_interrupt_randomness(int irq); * void add_input_randomness(unsigned int type, unsigned int code, unsigned int value); @@ -696,10 +695,6 @@ static void __cold _credit_init_bits(size_t bits) * entropy as specified by the caller. If the entropy pool is full it will * block until more entropy is needed. * - * add_bootloader_randomness() is called by bootloader drivers, such as EFI - * and device tree, and credits its input depending on whether or not the - * configuration option CONFIG_RANDOM_TRUST_BOOTLOADER is set. - * * add_vmfork_randomness() adds a unique (but not necessarily secret) ID * representing the current instance of a VM to the pool, without crediting, * and then force-reseeds the crng so that it takes effect immediately. @@ -765,6 +760,18 @@ static int random_pm_notification(struct notifier_block *nb, unsigned long actio static struct notifier_block pm_notifier = { .notifier_call = random_pm_notification }; +/* + * Handle random seed passed by bootloader. The buf pointer + * must remain alive during the kernel's init sequence. + */ +static __initdata const void *bootloader_seed; +static __initdata size_t bootloader_seed_bytes; +void __init register_bootloader_seed(const void *buf, size_t len) +{ + bootloader_seed = buf; + bootloader_seed_bytes = len; +} + /* * The first collection of entropy occurs at system boot while interrupts * are still turned off. Here we push in latent entropy, RDSEED, a timestamp, @@ -793,6 +800,8 @@ int __init random_init(const char *command_line) } _mix_pool_bytes(&entropy, sizeof(entropy)); } + if (bootloader_seed && bootloader_seed_bytes) + _mix_pool_bytes(bootloader_seed, bootloader_seed_bytes); _mix_pool_bytes(&now, sizeof(now)); _mix_pool_bytes(utsname(), sizeof(*(utsname()))); _mix_pool_bytes(command_line, strlen(command_line)); @@ -800,9 +809,10 @@ int __init random_init(const char *command_line) if (crng_ready()) crng_reseed(); - else if (trust_cpu) - _credit_init_bits(arch_bytes * 8); - used_arch_random = arch_bytes * 8 >= POOL_READY_BITS; + else + _credit_init_bits((trust_cpu ? arch_bytes * 8 : 0) + + (trust_bootloader ? bootloader_seed_bytes * 8 : 0)); + used_arch_random = arch_bytes * 8 + bootloader_seed_bytes * 8 >= POOL_READY_BITS; WARN_ON(register_pm_notifier(&pm_notifier)); @@ -861,18 +871,6 @@ void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy) } EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); -/* - * Handle random seed passed by bootloader, and credit it if - * CONFIG_RANDOM_TRUST_BOOTLOADER is set. - */ -void __cold add_bootloader_randomness(const void *buf, size_t len) -{ - mix_pool_bytes(buf, len); - if (trust_bootloader) - credit_init_bits(len * 8); -} -EXPORT_SYMBOL_GPL(add_bootloader_randomness); - #if IS_ENABLED(CONFIG_VMGENID) static BLOCKING_NOTIFIER_HEAD(vmfork_chain); diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c index 860534bcfdac..daf374983012 100644 --- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -614,7 +614,7 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables, sizeof(*seed) + size); if (seed != NULL) { pr_notice("seeding entropy pool\n"); - add_bootloader_randomness(seed->bits, size); + register_bootloader_seed(seed->bits, size); early_memunmap(seed, sizeof(*seed) + size); } else { pr_err("Could not map UEFI random seed!\n"); diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c index a8f5b6532165..389ef0f781c2 100644 --- a/drivers/of/fdt.c +++ b/drivers/of/fdt.c @@ -1201,7 +1201,7 @@ int __init early_init_dt_scan_chosen(char *cmdline) rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l); if (rng_seed && l > 0) { - add_bootloader_randomness(rng_seed, l); + register_bootloader_seed(rng_seed, l); /* try to clear seed so it won't be found. */ fdt_nop_property(initial_boot_params, node, "rng-seed"); diff --git a/include/linux/random.h b/include/linux/random.h index fae0c84027fd..c4fa7ca008df 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -13,7 +13,6 @@ struct notifier_block; void add_device_randomness(const void *buf, size_t len); -void add_bootloader_randomness(const void *buf, size_t len); void add_input_randomness(unsigned int type, unsigned int code, unsigned int value) __latent_entropy; void add_interrupt_randomness(int irq) __latent_entropy; @@ -72,6 +71,7 @@ static inline unsigned long get_random_canary(void) return get_random_long() & CANARY_MASK; } +void __init register_bootloader_seed(const void *buf, size_t len); int __init random_init(const char *command_line); bool rng_is_initialized(void); bool rng_has_arch_random(void);
Stephen reported that a static key warning splat appears during early boot on systems that credit randomness from device trees that contain an "rng-seed" property, because because setup_machine_fdt() is called before jump_label_init() during setup_arch(): static_key_enable_cpuslocked(): static key '0xffffffe51c6fcfc0' used before call to jump_label_init() WARNING: CPU: 0 PID: 0 at kernel/jump_label.c:166 static_key_enable_cpuslocked+0xb0/0xb8 Modules linked in: CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0+ #224 44b43e377bfc84bc99bb5ab885ff694984ee09ff pstate: 600001c9 (nZCv dAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : static_key_enable_cpuslocked+0xb0/0xb8 lr : static_key_enable_cpuslocked+0xb0/0xb8 sp : ffffffe51c393cf0 x29: ffffffe51c393cf0 x28: 000000008185054c x27: 00000000f1042f10 x26: 0000000000000000 x25: 00000000f10302b2 x24: 0000002513200000 x23: 0000002513200000 x22: ffffffe51c1c9000 x21: fffffffdfdc00000 x20: ffffffe51c2f0831 x19: ffffffe51c6fcfc0 x18: 00000000ffff1020 x17: 00000000e1e2ac90 x16: 00000000000000e0 x15: ffffffe51b710708 x14: 0000000000000066 x13: 0000000000000018 x12: 0000000000000000 x11: 0000000000000000 x10: 00000000ffffffff x9 : 0000000000000000 x8 : 0000000000000000 x7 : 61632065726f6665 x6 : 6220646573752027 x5 : ffffffe51c641d25 x4 : ffffffe51c13142c x3 : ffff0a00ffffff05 x2 : 40000000ffffe003 x1 : 00000000000001c0 x0 : 0000000000000065 Call trace: static_key_enable_cpuslocked+0xb0/0xb8 static_key_enable+0x2c/0x40 crng_set_ready+0x24/0x30 execute_in_process_context+0x80/0x90 _credit_init_bits+0x100/0x154 add_bootloader_randomness+0x64/0x78 early_init_dt_scan_chosen+0x140/0x184 early_init_dt_scan_nodes+0x28/0x4c early_init_dt_scan+0x40/0x44 setup_machine_fdt+0x7c/0x120 setup_arch+0x74/0x1d8 start_kernel+0x84/0x44c __primary_switched+0xc0/0xc8 ---[ end trace 0000000000000000 ]--- random: crng init done Machine model: Google Lazor (rev1 - 2) with LTE A trivial fix went in to address this on arm64, 73e2d827a501 ("arm64: Initialize jump labels before setup_machine_fdt()"). But it appears that fixing it on other platforms might not be so trivial. And in the past there have been problems related to add_bootloader_randomness() being called too early in boot for what it needed. This patch defers all entropy crediting until random_init(), where we can be sure that all facilities we need are up and running. It changes the name add_bootloader_randomness() to register_bootloader_seed(), and insists that its buffer remain alive during all of __init. A potential downside is that EFI runs a little bit before random_init(), which means we were getting that seed a lot earlier before. Fixes: f5bda35fba61 ("random: use static branch for crng_ready()") Reported-by: Stephen Boyd <swboyd@chromium.org> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Phil Elwell <phil@raspberrypi.com> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- Ard - I guess we've got two things to figure out here: 1) How much we gain by the situation before this patch of EFI supplying its seed before random_init(). 2) Whether those buffers are guaranteed to live throughout __init, or if this patch introduces a UaF. -Jason drivers/char/random.c | 38 ++++++++++++++++++-------------------- drivers/firmware/efi/efi.c | 2 +- drivers/of/fdt.c | 2 +- include/linux/random.h | 2 +- 4 files changed, 21 insertions(+), 23 deletions(-)