powerpc/vdso: Don't map VDSO at a fixed address on PPC32

PPC64 removed default mapping address from VDSO in
commit 30d0b3682887 ("powerpc: Move 64bit VDSO to improve context
switch performance").

Do like PPC64 and let get_unmapped_area() place the VDSO mapping
at the address it wants, don't force a default address.

This allows randomisation of VDSO address.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/cba76f5a5b01fcc49415e632d92c11c1c5998cab.1660843877.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/include/asm/vdso.h b/arch/powerpc/include/asm/vdso.h
index 8542e9b..7650b6c 100644 (file)
--- a/arch/powerpc/include/asm/vdso.h
+++ b/arch/powerpc/include/asm/vdso.h
@@ -2,9 +2,6 @@
 #ifndef _ASM_POWERPC_VDSO_H
 #define _ASM_POWERPC_VDSO_H
 
-/* Default map addresses for 32bit vDSO */
-#define VDSO32_MBASE   0x100000
-
 #define VDSO_VERSION_STRING    LINUX_2.6.15
 
 #ifndef __ASSEMBLY__

diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 0da2875..bf9574e 100644 (file)
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -200,28 +200,19 @@ static int __arch_setup_additional_pages(struct linux_binprm *bprm, int uses_int
        if (is_32bit_task()) {
                vdso_spec = &vdso32_spec;
                vdso_size = &vdso32_end - &vdso32_start;
-               vdso_base = VDSO32_MBASE;
        } else {
                vdso_spec = &vdso64_spec;
                vdso_size = &vdso64_end - &vdso64_start;
-               /*
-                * On 64bit we don't have a preferred map address. This
-                * allows get_unmapped_area to find an area near other mmaps
-                * and most likely share a SLB entry.
-                */
-               vdso_base = 0;
        }
 
        mappings_size = vdso_size + vvar_size;
        mappings_size += (VDSO_ALIGNMENT - 1) & PAGE_MASK;
 
        /*
-        * pick a base address for the vDSO in process space. We try to put it
-        * at vdso_base which is the "natural" base for it, but we might fail
-        * and end up putting it elsewhere.
+        * Pick a base address for the vDSO in process space.
         * Add enough to the size so that the result can be aligned.
         */
-       vdso_base = get_unmapped_area(NULL, vdso_base, mappings_size, 0, 0);
+       vdso_base = get_unmapped_area(NULL, 0, mappings_size, 0, 0);
        if (IS_ERR_VALUE(vdso_base))
                return vdso_base;