Messages in this thread Patch in this message | | | Date | Mon, 30 Mar 2020 17:38:01 +0000 | From | George Spelvin <> | Subject | [PATCH v2] arm64: kexec_file: Avoid temp buffer for RNG seed |
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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 --- v2: Typos in commit message fixed.
Thank you, I'd be delighted if you'd apply it to the arm64 tree directly! I can take it out of my patch series and off my plate.
Now that I'm looking at it some more, I want to change fdt_setprop_placeholder to return an ERR_PTR. Must. Stop. Scope. Creep.
arch/arm64/kernel/machine_kexec_file.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c index 7b08bf9499b6b..69e25bb96e3fb 100644 --- a/arch/arm64/kernel/machine_kexec_file.c +++ b/arch/arm64/kernel/machine_kexec_file.c @@ -106,12 +106,12 @@ 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); -- 2.26.0
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