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@@ -0,0 +1,74 @@
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+From 4cef2fc7308b2132317ad166939994f098b41561 Mon Sep 17 00:00:00 2001
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+From: Ross Burton <ross.burton@arm.com>
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+Date: Tue, 9 Sep 2025 14:23:14 +0100
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+Subject: [PATCH] CVE-2024-56738
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+
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+Backport an algorithmic change to grub_crypto_memcmp() so that it completes in
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+constant time and thus isn't susceptible to side-channel attacks.
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+
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+This is a partial backport of grub 0739d24cd
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+("libgcrypt: Adjust import script, definitions and API users for libgcrypt 1.11")
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+
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+CVE: CVE-2024-56738
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+Upstream-Status: Backport [0739d24cd]
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+Signed-off-by: Ross Burton <ross.burton@arm.com>
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+---
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+ grub-core/lib/crypto.c | 23 ++++++++++++++++-------
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+ include/grub/crypto.h | 2 +-
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+ 2 files changed, 17 insertions(+), 8 deletions(-)
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+
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+diff --git a/grub-core/lib/crypto.c b/grub-core/lib/crypto.c
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+index 396f76410..19db7870a 100644
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+--- a/grub-core/lib/crypto.c
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++++ b/grub-core/lib/crypto.c
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+@@ -433,19 +433,28 @@ grub_crypto_gcry_error (gcry_err_code_t in)
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+ return GRUB_ACCESS_DENIED;
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+ }
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+
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++/*
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++ * Compare byte arrays of length LEN, return 1 if it's not same,
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++ * 0, otherwise.
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++ */
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+ int
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+-grub_crypto_memcmp (const void *a, const void *b, grub_size_t n)
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++grub_crypto_memcmp (const void *b1, const void *b2, grub_size_t len)
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+ {
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+- register grub_size_t counter = 0;
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+- const grub_uint8_t *pa, *pb;
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++ const grub_uint8_t *a = b1;
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++ const grub_uint8_t *b = b2;
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++ int ab, ba;
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++ grub_size_t i;
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+
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+- for (pa = a, pb = b; n; pa++, pb++, n--)
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++ /* Constant-time compare. */
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++ for (i = 0, ab = 0, ba = 0; i < len; i++)
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+ {
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+- if (*pa != *pb)
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+- counter++;
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++ /* If a[i] != b[i], either ab or ba will be negative. */
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++ ab |= a[i] - b[i];
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++ ba |= b[i] - a[i];
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+ }
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+
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+- return !!counter;
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++ /* 'ab | ba' is negative when buffers are not equal, extract sign bit. */
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++ return ((unsigned int)(ab | ba) >> (sizeof(unsigned int) * 8 - 1)) & 1;
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+ }
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+
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+ #ifndef GRUB_UTIL
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+diff --git a/include/grub/crypto.h b/include/grub/crypto.h
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+index 31c87c302..20ad4c5f7 100644
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+--- a/include/grub/crypto.h
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++++ b/include/grub/crypto.h
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+@@ -393,7 +393,7 @@ grub_crypto_pbkdf2 (const struct gcry_md_spec *md,
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+ grub_uint8_t *DK, grub_size_t dkLen);
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+
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+ int
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+-grub_crypto_memcmp (const void *a, const void *b, grub_size_t n);
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++grub_crypto_memcmp (const void *b1, const void *b2, grub_size_t len);
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+
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+ int
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+ grub_password_get (char buf[], unsigned buf_size);
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+--
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+2.43.0
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Ross Burton