Commit 99ee28d9 authored Mar 30, 2020 by George Spelvin Committed by Will Deacon Apr 28, 2020

arm64: kexec_file: Avoid temp buffer for RNG seed



After using get_random_bytes(), you want to wipe the buffer
afterward so the seed remains secret.

In this case, we can eliminate the temporary buffer entirely.
fdt_setprop_placeholder() returns a pointer to the property value
buffer, allowing us to put the random data directly in there without
using a temporary buffer at all.  Faster and less stack all in one.

Signed-off-by: George Spelvin <lkml@sdf.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20200330173801.GA9199@SDF.ORG


Signed-off-by: Will Deacon <will@kernel.org>

parent 348a625d

arch/arm64/kernel/machine_kexec_file.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -138,12 +138,12 @@ static int setup_dtb(struct kimage *image,

		/* add rng-seed */
		if (rng_is_initialized()) {
		u8 rng_seed[RNG_SEED_SIZE];
		get_random_bytes(rng_seed, RNG_SEED_SIZE);
		ret = fdt_setprop(dtb, off, FDT_PROP_RNG_SEED, rng_seed,
		RNG_SEED_SIZE);
		void *rng_seed;
		ret = fdt_setprop_placeholder(dtb, off, FDT_PROP_RNG_SEED,
		RNG_SEED_SIZE, &rng_seed);
		if (ret)
		goto out;
		get_random_bytes(rng_seed, RNG_SEED_SIZE);
		} else {
		pr_notice("RNG is not initialised: omitting \"%s\" property\n",
		FDT_PROP_RNG_SEED);

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