mm: make arch_get_unmapped_area() take vm_flags by default

Patch series "mm: Care about shadow stack guard gap when getting an
unmapped area", v2.

As covered in the commit log for c44357c2e76b ("x86/mm: care about shadow
stack guard gap during placement") our current mmap() implementation does
not take care to ensure that a new mapping isn't placed with existing
mappings inside it's own guard gaps.  This is particularly important for
shadow stacks since if two shadow stacks end up getting placed adjacent to
each other then they can overflow into each other which weakens the
protection offered by the feature.

On x86 there is a custom arch_get_unmapped_area() which was updated by the
above commit to cover this case by specifying a start_gap for allocations
with VM_SHADOW_STACK.  Both arm64 and RISC-V have equivalent features and
use the generic implementation of arch_get_unmapped_area() so let's make
the equivalent change there so they also don't get shadow stack pages
placed without guard pages.  The arm64 and RISC-V shadow stack
implementations are currently on the list:

   https://lore.kernel.org/r/20240829-arm64-gcs-v12-0-42fec94743
   https://lore.kernel.org/lkml/20240403234054.2020347-1-debug@rivosinc.com/

Given the addition of the use of vm_flags in the generic implementation we
also simplify the set of possibilities that have to be dealt with in the
core code by making arch_get_unmapped_area() take vm_flags as standard. 
This is a bit invasive since the prototype change touches quite a few
architectures but since the parameter is ignored the change is
straightforward, the simplification for the generic code seems worth it.


This patch (of 3):

When we introduced arch_get_unmapped_area_vmflags() in 961148704acd ("mm:
introduce arch_get_unmapped_area_vmflags()") we did so as part of properly
supporting guard pages for shadow stacks on x86_64, which uses a custom
arch_get_unmapped_area().  Equivalent features are also present on both
arm64 and RISC-V, both of which use the generic implementation of
arch_get_unmapped_area() and will require equivalent modification there. 
Rather than continue to deal with having two versions of the functions
let's bite the bullet and have all implementations of
arch_get_unmapped_area() take vm_flags as a parameter.

The new parameter is currently ignored by all implementations other than
x86.  The only caller that doesn't have a vm_flags available is
mm_get_unmapped_area(), as for the x86 implementation and the wrapper used
on other architectures this is modified to supply no flags.

No functional changes.

Link: https://lkml.kernel.org/r/20240904-mm-generic-shadow-stack-guard-v2-0-a46b8b6dc0ed@kernel.org
Link: https://lkml.kernel.org/r/20240904-mm-generic-shadow-stack-guard-v2-1-a46b8b6dc0ed@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Acked-by: Helge Deller <deller@gmx.de>	[parisc]
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Chris Zankel <chris@zankel.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N Rao <naveen@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Rich Felker <dalias@libc.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 7 insertions, 24 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 02f7b45c3076..98249266196e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -770,7 +770,7 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr,
 unsigned long
 arch_get_unmapped_area(struct file *filp, unsigned long addr,
 		       unsigned long len, unsigned long pgoff,
-		       unsigned long flags)
+		       unsigned long flags, vm_flags_t vm_flags)
 {
 	return generic_get_unmapped_area(filp, addr, len, pgoff, flags);
 }
@@ -834,38 +834,21 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
 unsigned long
 arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
 			       unsigned long len, unsigned long pgoff,
-			       unsigned long flags)
+			       unsigned long flags, vm_flags_t vm_flags)
 {
 	return generic_get_unmapped_area_topdown(filp, addr, len, pgoff, flags);
 }
 #endif
 
-#ifndef HAVE_ARCH_UNMAPPED_AREA_VMFLAGS
-unsigned long
-arch_get_unmapped_area_vmflags(struct file *filp, unsigned long addr, unsigned long len,
-			       unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
-{
-	return arch_get_unmapped_area(filp, addr, len, pgoff, flags);
-}
-
-unsigned long
-arch_get_unmapped_area_topdown_vmflags(struct file *filp, unsigned long addr,
-				       unsigned long len, unsigned long pgoff,
-				       unsigned long flags, vm_flags_t vm_flags)
-{
-	return arch_get_unmapped_area_topdown(filp, addr, len, pgoff, flags);
-}
-#endif
-
 unsigned long mm_get_unmapped_area_vmflags(struct mm_struct *mm, struct file *filp,
 					   unsigned long addr, unsigned long len,
 					   unsigned long pgoff, unsigned long flags,
 					   vm_flags_t vm_flags)
 {
 	if (test_bit(MMF_TOPDOWN, &mm->flags))
-		return arch_get_unmapped_area_topdown_vmflags(filp, addr, len, pgoff,
-							      flags, vm_flags);
-	return arch_get_unmapped_area_vmflags(filp, addr, len, pgoff, flags, vm_flags);
+		return arch_get_unmapped_area_topdown(filp, addr, len, pgoff,
+						      flags, vm_flags);
+	return arch_get_unmapped_area(filp, addr, len, pgoff, flags, vm_flags);
 }
 
 unsigned long
@@ -927,8 +910,8 @@ mm_get_unmapped_area(struct mm_struct *mm, struct file *file,
 		     unsigned long pgoff, unsigned long flags)
 {
 	if (test_bit(MMF_TOPDOWN, &mm->flags))
-		return arch_get_unmapped_area_topdown(file, addr, len, pgoff, flags);
-	return arch_get_unmapped_area(file, addr, len, pgoff, flags);
+		return arch_get_unmapped_area_topdown(file, addr, len, pgoff, flags, 0);
+	return arch_get_unmapped_area(file, addr, len, pgoff, flags, 0);
 }
 EXPORT_SYMBOL(mm_get_unmapped_area);