Messages in this thread | | | Date | Fri, 7 Aug 2020 11:17:23 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] arm64: kaslr: Use standard early random function |
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Hi Guenter,
On Thu, Aug 06, 2020 at 05:49:04PM -0700, Guenter Roeck wrote: > Commit 585524081ecd ("random: random.h should include archrandom.h, not > the other way around") tries to fix a problem with recursive inclusion > of linux/random.h and arch/archrandom.h for arm64. Unfortunately, this > results in the following compile error if ARCH_RANDOM is disabled. > > arch/arm64/kernel/kaslr.c: In function 'kaslr_early_init': > arch/arm64/kernel/kaslr.c:128:6: error: implicit declaration of function > '__early_cpu_has_rndr'; did you mean '__early_pfn_to_nid'? > [-Werror=implicit-function-declaration] > if (__early_cpu_has_rndr()) { > ^~~~~~~~~~~~~~~~~~~~ > __early_pfn_to_nid > arch/arm64/kernel/kaslr.c:131:7: error: implicit declaration of function > '__arm64_rndr' [-Werror=implicit-function-declaration] > if (__arm64_rndr(&raw)) > ^~~~~~~~~~~~ > > Problem is that arch/archrandom.h is only included from linux/random.h if > ARCH_RANDOM is enabled. If not, __arm64_rndr() and __early_cpu_has_rndr() > are undeclared, causing the problem. > > Use arch_get_random_seed_long_early() instead of arm64 specific functions > to solve the problem. As a side effect of this change, the code no longer > bypasses ARCH_RANDOM, which I consider desirable (after all, ARCH_RANDOM > was disabled for a reason).
There's no bypass of ARCH_RANDOM; the bits KASLR depends on are empty stubs when ARCH_RANDOM is not selected. I added the common early functions after this code was written.
> Reported-by: Qian Cai <cai@lca.pw> > Fixes: 585524081ecd ("random: random.h should include archrandom.h, not the other way around")
This is where things broke; there was no need to change kaslr.c's include of <asm/archrandom.h>, since kaslr.c only depends on the RNDR bits defined there./
> Fixes: 2e8e1ea88cbc ("arm64: Use v8.5-RNG entropy for KASLR seed")
I don't think this tag is necessary; this commit built and worked fine, and there wasn't any ARCH_RANDOM bypass to speak of.
> Cc: Qian Cai <cai@lca.pw> > Cc: Mark Brown <broonie@kernel.org> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This patch itself looks fine, but as above I think the commit message is misleading w.r.t. bypassing ARCH_RANDOM, and the second fixes tag isn't necessary.
With those bits gone:
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Mark.
> --- > arch/arm64/kernel/kaslr.c | 12 +++++------- > 1 file changed, 5 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c > index 9ded4237e1c1..b181e0544b79 100644 > --- a/arch/arm64/kernel/kaslr.c > +++ b/arch/arm64/kernel/kaslr.c > @@ -84,6 +84,7 @@ u64 __init kaslr_early_init(u64 dt_phys) > void *fdt; > u64 seed, offset, mask, module_range; > const u8 *cmdline, *str; > + unsigned long raw; > int size; > > /* > @@ -122,15 +123,12 @@ u64 __init kaslr_early_init(u64 dt_phys) > } > > /* > - * Mix in any entropy obtainable architecturally, open coded > - * since this runs extremely early. > + * Mix in any entropy obtainable architecturally if enabled > + * and supported. > */ > - if (__early_cpu_has_rndr()) { > - unsigned long raw; > > - if (__arm64_rndr(&raw)) > - seed ^= raw; > - } > + if (arch_get_random_seed_long_early(&raw)) > + seed ^= raw; > > if (!seed) { > kaslr_status = KASLR_DISABLED_NO_SEED; > -- > 2.17.1 >
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