linux-kernel - [PATCH 2/2] riscv: mm: Update mmap_rnd_bits

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Message-ID: <20230929211155.3910949-6-samitolvanen@google.com>
Date:   Fri, 29 Sep 2023 21:11:58 +0000
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
Cc:     linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 2/2] riscv: mm: Update mmap_rnd_bits_max

ARCH_MMAP_RND_BITS_MAX is based on Sv39, which leaves a few
potential bits of mmap randomness on the table if we end up enabling
4/5-level paging. Update mmap_rnd_bits_max to take the final address
space size into account. This increases mmap_rnd_bits_max from 24 to
33 with Sv48/57.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 arch/riscv/mm/init.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 0798bd861dcb..ff8d21a6cb2d 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -762,6 +762,11 @@ static int __init print_no5lvl(char *p)
 }
 early_param("no5lvl", print_no5lvl);
 
+static void __init set_mmap_rnd_bits_max(void)
+{
+	mmap_rnd_bits_max = MMAP_VA_BITS - PAGE_SHIFT - 3;
+}
+
 /*
  * There is a simple way to determine if 4-level is supported by the
  * underlying hardware: establish 1:1 mapping in 4-level page table mode
@@ -1071,6 +1076,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 
 #if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL)
 	set_satp_mode(dtb_pa);
+	set_mmap_rnd_bits_max();
 #endif
 
 	/*
-- 
2.42.0.582.g8ccd20d70d-goog