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From: Amanieu d'Antras <amanieu@gmail.com>
Cc: Amanieu d'Antras <amanieu@gmail.com>,
	Ryan Houdek <Houdek.Ryan@fex-emu.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Steven Price <steven.price@arm.com>,
	Arnd Bergmann <arnd@kernel.org>,
	David Laight <David.Laight@aculab.com>,
	Mark Brown <broonie@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: [RESEND PATCH v4 3/8] mm: Support mmap_compat_base with the generic layout
Date: Tue, 18 May 2021 10:06:53 +0100	[thread overview]
Message-ID: <20210518090658.9519-4-amanieu@gmail.com> (raw)
In-Reply-To: <20210518090658.9519-1-amanieu@gmail.com>

This enables architectures using the generic mmap layout to support
32-bit mmap calls from 64-bit processes and vice-versa.

Architectures using this must define separate 32-bit and 64-bit versions
of STACK_TOP, TASK_UNMAPPED_BASE and STACK_RND_MASK.

Signed-off-by: Amanieu d'Antras <amanieu@gmail.com>
Co-developed-by: Ryan Houdek <Houdek.Ryan@fex-emu.org>
Signed-off-by: Ryan Houdek <Houdek.Ryan@fex-emu.org>
---
 mm/util.c | 46 ++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 8 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 54870226cea6..37bd764174b5 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -353,12 +353,12 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 	return randomize_page(mm->brk, SZ_1G);
 }
 
-unsigned long arch_mmap_rnd(void)
+static unsigned long mmap_rnd(bool compat)
 {
 	unsigned long rnd;
 
 #ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
-	if (is_compat_task())
+	if (compat)
 		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
 	else
 #endif /* CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS */
@@ -367,6 +367,11 @@ unsigned long arch_mmap_rnd(void)
 	return rnd << PAGE_SHIFT;
 }
 
+unsigned long arch_mmap_rnd(void)
+{
+	return mmap_rnd(is_compat_task());
+}
+
 static int mmap_is_legacy(struct rlimit *rlim_stack)
 {
 	if (current->personality & ADDR_COMPAT_LAYOUT)
@@ -383,16 +388,17 @@ static int mmap_is_legacy(struct rlimit *rlim_stack)
  * the face of randomisation.
  */
 #define MIN_GAP		(SZ_128M)
-#define MAX_GAP		(STACK_TOP / 6 * 5)
+#define MAX_GAP		(stack_top / 6 * 5)
 
-static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
+static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack,
+	unsigned long stack_top, unsigned long stack_rnd_mask)
 {
 	unsigned long gap = rlim_stack->rlim_cur;
 	unsigned long pad = stack_guard_gap;
 
 	/* Account for stack randomization if necessary */
 	if (current->flags & PF_RANDOMIZE)
-		pad += (STACK_RND_MASK << PAGE_SHIFT);
+		pad += (stack_rnd_mask << PAGE_SHIFT);
 
 	/* Values close to RLIM_INFINITY can overflow. */
 	if (gap + pad > gap)
@@ -403,21 +409,45 @@ static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
 	else if (gap > MAX_GAP)
 		gap = MAX_GAP;
 
-	return PAGE_ALIGN(STACK_TOP - gap - rnd);
+	return PAGE_ALIGN(stack_top - gap - rnd);
 }
 
 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	unsigned long random_factor = 0UL;
+#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
+	unsigned long compat_random_factor = 0UL;
+#endif
 
-	if (current->flags & PF_RANDOMIZE)
+	if (current->flags & PF_RANDOMIZE) {
+#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
+		random_factor = mmap_rnd(false);
+		compat_random_factor = mmap_rnd(true);
+#else
 		random_factor = arch_mmap_rnd();
+#endif
+	}
 
 	if (mmap_is_legacy(rlim_stack)) {
+#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
+		mm->mmap_base = TASK_UNMAPPED_BASE_64 + random_factor;
+		mm->mmap_compat_base =
+			TASK_UNMAPPED_BASE_32 + compat_random_factor;
+#else
 		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
+#endif
 		mm->get_unmapped_area = arch_get_unmapped_area;
 	} else {
-		mm->mmap_base = mmap_base(random_factor, rlim_stack);
+#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
+		mm->mmap_base = mmap_base(random_factor, rlim_stack,
+					  STACK_TOP_64, STACK_RND_MASK_64);
+		mm->mmap_compat_base = mmap_base(compat_random_factor,
+						 rlim_stack, STACK_TOP_32,
+						 STACK_RND_MASK_32);
+#else
+		mm->mmap_base = mmap_base(random_factor, rlim_stack, STACK_TOP,
+					  STACK_RND_MASK);
+#endif
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 	}
 }
-- 
2.31.1


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  parent reply	other threads:[~2021-05-18  9:10 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-18  9:06 [RESEND PATCH v4 0/8] arm64: Allow 64-bit tasks to invoke compat syscalls Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 1/8] mm: Add arch_get_mmap_base_topdown macro Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 2/8] hugetlbfs: Use arch_get_mmap_* macros Amanieu d'Antras
2021-05-18  9:06 ` Amanieu d'Antras [this message]
2021-05-18  9:06 ` [RESEND PATCH v4 4/8] arm64: Separate in_compat_syscall from is_compat_task Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 5/8] arm64: mm: Use HAVE_ARCH_COMPAT_MMAP_BASES Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 6/8] arm64: Add a compat syscall flag to thread_info Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 7/8] arm64: Forbid calling compat sigreturn from 64-bit tasks Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 8/8] arm64: Allow 64-bit tasks to invoke compat syscalls Amanieu d'Antras
2021-05-18 13:02   ` Arnd Bergmann
2021-05-18 20:26     ` David Laight
2021-05-18 22:41       ` Ryan Houdek
2021-05-18 23:51     ` Amanieu d'Antras
2021-05-19 15:30       ` Steven Price
2021-05-19 16:14         ` Amanieu d'Antras
2021-05-21  8:51           ` Steven Price
2021-05-21 19:18             ` Amanieu d'Antras
2021-05-24 11:20               ` Steven Price
2021-05-24 12:38                 ` David Laight
2021-05-18 23:52     ` Ryan Houdek

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