Commit c4f1b56f authored by Lorenzo Stoakes's avatar Lorenzo Stoakes Committed by Andrew Morton
Browse files

mips: vdso: prefer do_mmap() to mmap_region() 

Patch series "mm: update mips to use do_mmap(), make mmap_region()
internal".

Currently the only user of mmap_region() outside of the memory management
code is the MIPS VDSO implementation.

This uses mmap_region() to map a 'delay slot emulation page' at the top of
the stack which is read-only and executable.

This mapping requires that an already-acquired mmap write lock is utilised
and that uffd and populate logic is ignored. This rules out vm_mmap(),
however do_mmap() fits the bill.

Adapt this code to use do_mmap() and then once done, make mmap_region()
internal and userland testable, and avoid any other uses of mmap_region(),
which is absolutely and strictly an internal mm function which bypasses a
great number of checks and logic.


This patch (of 2):

mmap_region() is an internal memory management implementation detail that
is not intended to be used outside of the memory management subsystem.

Map the delay slot emulation page using do_mmap() which makes use of the
already-held mmap write lock and bypasses unneeded populate and
userfaultfd logic.

This should have the precise same behaviour as the existing logic.

Link: https://lkml.kernel.org/r/cover.1735819274.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/ef076e381570f709e5c2c142dc030ec5b3309a0e.1735819274.git.lorenzo.stoakes@oracle.com


Signed-off-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: default avatarLiam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4f79384a

arch/mips/kernel/vdso.c

+6 −4
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <linux/ioport.h>

#include <linux/kernel.h>

#include <linux/mm.h>

#include <linux/mman.h>

#include <linux/random.h>

#include <linux/sched.h>

#include <linux/slab.h>
@@ -97,11 +98,12 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp) 
		return -EINTR;



	if (IS_ENABLED(CONFIG_MIPS_FP_SUPPORT)) {

		unsigned long unused;



		/* Map delay slot emulation page */

		base = mmap_region(NULL, STACK_TOP, PAGE_SIZE,

				VM_READ | VM_EXEC |

				VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,

				0, NULL);

		base = do_mmap(NULL, STACK_TOP, PAGE_SIZE, PROT_READ | PROT_EXEC,

			       MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, 0, 0, &unused,

			       NULL);

		if (IS_ERR_VALUE(base)) {

			ret = base;

			goto out;