5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
[ 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>
---
arch/x86/kernel/process.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index b8de27bb6e09c..c402b079b74e8 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -793,7 +793,10 @@ 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);
}
/*
--
2.43.0
