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Peter Anvin" , Peter Zijlstra , Qi Zheng , Alexandre Ghiti , x86@kernel.org, Al Viro , Christian Brauner , Jan Kara , Eric Biederman , Christophe Leroy , Josh Poimboeuf , "Kirill A. Shutemov" , Rick Edgecombe , Brian Gerst , Bjorn Helgaas , Tony Battersby , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: [PATCH 1/2] x86: Increase brk randomness entropy on x86_64 Date: Fri, 16 Feb 2024 22:25:43 -0800 Message-Id: <20240217062545.1631668-1-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240217062035.work.493-kees@kernel.org> References: <20240217062035.work.493-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1595; i=keescook@chromium.org; h=from:subject; bh=J8yZ3FuS1LWrR5jVIrwba2SyB7GFZoxGQ5Gq7wzczYA=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBl0FFofylSSc0zctidXuws91GIZAfUD3EvfMTgD C7ILFWiQEWJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZdBRaAAKCRCJcvTf3G3A JuvKD/0YST+WQlVawQvhCb3pQXdND3wneO4rAAc1MIaPKKYFGzOMCeSQYBifV0JEeFHph1WsrQC n4+hCw/MTLwSm24DnSu1EEevAaPtL2voVeq16UMZrkG/yapEWn3+250s3daI8qSEHpaTs+lqmrY 20PeyS18a3NDnzD6VRtlc/Ud4NM4lTrD59tsR9Zypsk8QkTOW11SzkDOU36Vewr5lvz9WlASgCb uX115bQ6YNYuZQkpWi0z4MlnmeNcdOuQnupP0FwTKJDVMHrN+vvFac+rR68LNoQtHQMqb0yZKXr iaQfIX0RbdI1t7Ns/XMSdQQfLgvkslY3PnQ7KanuL/2iVQSA+qYKaUHT1q5rU9VB+w3Dck4Dmye Mw0zNvdQB8Y4A4EnGY6HYyO6ucLRSQtEfIuXbYYszYSq6wZmHI2F8gQrXTQN6dKrHavZBh6DOSY Ep4Xtnl5207P/j3tkJ2WlgxPesAECiupJebylL9V96dhr12EkUmNs83ixnDjhgIhd/q1C66ZLuD gOP5XrfxOIcEw0QQFj8sFRcjpHdAnouwZruQruo4ED1IAeSMX2ThvD6Di09uNBuIX4r27aUDkF4 PMMxi3r0jO2Iy/OhTCP2lOG3dtuz7BSAH3EaHzmxqr7QyGazjc6Mux/rumcsyyFjQTLaXMsCYg5 3MpCUeeX8WL+hxg== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1791126342497175598 X-GMAIL-MSGID: 1791126342497175598 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@gmail.com Closes: https://lore.kernel.org/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmus=dzOUG5E4gV7ayCbu0MPJTZzWkw@mail.gmail.com/ Signed-off-by: Kees Cook --- Cc: Jiri Kosina Cc: Geert Uytterhoeven Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Peter Zijlstra Cc: Qi Zheng Cc: Alexandre Ghiti Cc: x86@kernel.org --- 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 ab49ade31b0d..45a9d496fe2a 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); } /*