The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ea7e0480a4b695d0aa6b3fa99bd658a003122113 Mon Sep 17 00:00:00 2001

From: Paul Burton paul.burton@mips.com Date: Tue, 25 Sep 2018 15:51:26 -0700 Subject: [PATCH] MIPS: VDSO: Always map near top of user memory

When using the legacy mmap layout, for example triggered using ulimit -s unlimited, get_unmapped_area() fills memory from bottom to top starting from a fairly low address near TASK_UNMAPPED_BASE.

This placement is suboptimal if the user application wishes to allocate large amounts of heap memory using the brk syscall. With the VDSO being located low in the user's virtual address space, the amount of space available for access using brk is limited much more than it was prior to the introduction of the VDSO.

For example:

# ulimit -s unlimited; cat /proc/self/maps 00400000-004ec000 r-xp 00000000 08:00 71436 /usr/bin/coreutils 004fc000-004fd000 rwxp 000ec000 08:00 71436 /usr/bin/coreutils 004fd000-0050f000 rwxp 00000000 00:00 0 00cc3000-00ce4000 rwxp 00000000 00:00 0 [heap] 2ab96000-2ab98000 r--p 00000000 00:00 0 [vvar] 2ab98000-2ab99000 r-xp 00000000 00:00 0 [vdso] 2ab99000-2ab9d000 rwxp 00000000 00:00 0 ...

Resolve this by adjusting STACK_TOP to reserve space for the VDSO & providing an address hint to get_unmapped_area() causing it to use this space even when using the legacy mmap layout.

We reserve enough space for the VDSO, plus 1MB or 256MB for 32 bit & 64 bit systems respectively within which we randomize the VDSO base address. Previously this randomization was taken care of by the mmap base address randomization performed by arch_mmap_rnd(). The 1MB & 256MB sizes are somewhat arbitrary but chosen such that we have some randomization without taking up too much of the user's virtual address space, which is often in short supply for 32 bit systems.

With this the VDSO is always mapped at a high address, leaving lots of space for statically linked programs to make use of brk:

# ulimit -s unlimited; cat /proc/self/maps 00400000-004ec000 r-xp 00000000 08:00 71436 /usr/bin/coreutils 004fc000-004fd000 rwxp 000ec000 08:00 71436 /usr/bin/coreutils 004fd000-0050f000 rwxp 00000000 00:00 0 00c28000-00c49000 rwxp 00000000 00:00 0 [heap] ... 7f67c000-7f69d000 rwxp 00000000 00:00 0 [stack] 7f7fc000-7f7fd000 rwxp 00000000 00:00 0 7fcf1000-7fcf3000 r--p 00000000 00:00 0 [vvar] 7fcf3000-7fcf4000 r-xp 00000000 00:00 0 [vdso]

Signed-off-by: Paul Burton paul.burton@mips.com Reported-by: Huacai Chen chenhc@lemote.com Fixes: ebb5e78cc634 ("MIPS: Initial implementation of a VDSO") Cc: Huacai Chen chenhc@lemote.com Cc: linux-mips@linux-mips.org Cc: stable@vger.kernel.org # v4.4+

diff --git a/arch/mips/include/asm/processor.h b/arch/mips/include/asm/processor.h index b2fa62922d88..49d6046ca1d0 100644 --- a/arch/mips/include/asm/processor.h +++ b/arch/mips/include/asm/processor.h @@ -13,6 +13,7 @@

#include <linux/atomic.h> #include <linux/cpumask.h> +#include <linux/sizes.h> #include <linux/threads.h>

#include <asm/cachectl.h> @@ -80,11 +81,10 @@ extern unsigned int vced_count, vcei_count;

#endif

-/* - * One page above the stack is used for branch delay slot "emulation". - * See dsemul.c for details. - */ -#define STACK_TOP ((TASK_SIZE & PAGE_MASK) - PAGE_SIZE) +#define VDSO_RANDOMIZE_SIZE (TASK_IS_32BIT_ADDR ? SZ_1M : SZ_256M) + +extern unsigned long mips_stack_top(void); +#define STACK_TOP mips_stack_top()

/* * This decides where the kernel will search for a free chunk of vm diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c index 8fc69891e117..d4f7fd4550e1 100644 --- a/arch/mips/kernel/process.c +++ b/arch/mips/kernel/process.c @@ -32,6 +32,7 @@ #include <linux/nmi.h> #include <linux/cpu.h>

+#include <asm/abi.h> #include <asm/asm.h> #include <asm/bootinfo.h> #include <asm/cpu.h> @@ -39,6 +40,7 @@ #include <asm/dsp.h> #include <asm/fpu.h> #include <asm/irq.h> +#include <asm/mips-cps.h> #include <asm/msa.h> #include <asm/pgtable.h> #include <asm/mipsregs.h> @@ -645,6 +647,29 @@ unsigned long get_wchan(struct task_struct *task) return pc; }

+unsigned long mips_stack_top(void) +{ + unsigned long top = TASK_SIZE & PAGE_MASK; + + /* One page for branch delay slot "emulation" */ + top -= PAGE_SIZE; + + /* Space for the VDSO, data page & GIC user page */ + top -= PAGE_ALIGN(current->thread.abi->vdso->size); + top -= PAGE_SIZE; + top -= mips_gic_present() ? PAGE_SIZE : 0; + + /* Space for cache colour alignment */ + if (cpu_has_dc_aliases) + top -= shm_align_mask + 1; + + /* Space to randomize the VDSO base */ + if (current->flags & PF_RANDOMIZE) + top -= VDSO_RANDOMIZE_SIZE; + + return top; +} + /* * Don't forget that the stack pointer must be aligned on a 8 bytes * boundary for 32-bits ABI and 16 bytes for 64-bits ABI. diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c index 8f845f6e5f42..48a9c6b90e07 100644 --- a/arch/mips/kernel/vdso.c +++ b/arch/mips/kernel/vdso.c @@ -15,6 +15,7 @@ #include <linux/ioport.h> #include <linux/kernel.h> #include <linux/mm.h> +#include <linux/random.h> #include <linux/sched.h> #include <linux/slab.h> #include <linux/timekeeper_internal.h> @@ -97,6 +98,21 @@ void update_vsyscall_tz(void) } }

+static unsigned long vdso_base(void) +{ + unsigned long base; + + /* Skip the delay slot emulation page */ + base = STACK_TOP + PAGE_SIZE; + + if (current->flags & PF_RANDOMIZE) { + base += get_random_int() & (VDSO_RANDOMIZE_SIZE - 1); + base = PAGE_ALIGN(base); + } + + return base; +} + int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp) { struct mips_vdso_image *image = current->thread.abi->vdso; @@ -137,7 +153,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp) if (cpu_has_dc_aliases) size += shm_align_mask + 1;

- base = get_unmapped_area(NULL, 0, size, 0, 0); + base = get_unmapped_area(NULL, vdso_base(), size, 0, 0); if (IS_ERR_VALUE(base)) { ret = base; goto out;