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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>
This commit is contained in:
George Spelvin 2020-03-30 17:38:01 +00:00 committed by Will Deacon
parent 348a625dee
commit 99ee28d996
1 changed files with 4 additions and 4 deletions
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8
arch/arm64/kernel/machine_kexec_file.c
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@ -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);