This is a note to let you know that I've just added the patch titled
x86: Increase brk randomness entropy for 64-bit systems
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-increase-brk-randomness-entropy-for-64-bit-syste.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 14d3625c3effc0070c7f802c15da622eac9fd169
Author: Kees Cook <kees@xxxxxxxxxx>
Date: Fri Feb 16 22:25:43 2024 -0800
x86: Increase brk randomness entropy for 64-bit systems
[ Upstream commit 44c76825d6eefee9eb7ce06c38e1a6632ac7eb7d ]
In commit c1d171a00294 ("x86: randomize brk"), arch_randomize_brk() was
defined to use a 32MB range (13 bits of entropy), but was never increased
when moving to 64-bit. The default arch_randomize_brk() uses 32MB for
32-bit tasks, and 1GB (18 bits of entropy) for 64-bit tasks.
Update x86_64 to match the entropy used by arm64 and other 64-bit
architectures.
Reported-by: y0un9n132@xxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Jiri Kosina <jkosina@xxxxxxxx>
Closes: https://lore.kernel.org/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmus=dzOUG5E4gV7ayCbu0MPJTZzWkw@xxxxxxxxxxxxxx/
Link: https://lore.kernel.org/r/20240217062545.1631668-1-keescook@xxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index b6f4e8399fca2..5351f293f770b 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -1030,7 +1030,10 @@ unsigned long arch_align_stack(unsigned long sp)
unsigned long arch_randomize_brk(struct mm_struct *mm)
{
- return randomize_page(mm->brk, 0x02000000);
+ if (mmap_is_ia32())
+ return randomize_page(mm->brk, SZ_32M);
+
+ return randomize_page(mm->brk, SZ_1G);
}
/*
