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Message-ID: <520E8599.4080803@nod.at>
Date: Fri, 16 Aug 2013 22:03:37 +0200
From: Richard Weinberger <richard@....at>
To: Richard Weinberger <richard@....at>
CC: user-mode-linux-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, tj@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH] um: Implement probe_kernel_read()
Am 16.08.2013 21:44, schrieb Richard Weinberger:
> UML needs it's own probe_kernel_read() to handle kernel
> mode faults correctly.
> The implementation uses mincore() on the host side to detect
> whether a page is owned by the UML kernel process.
>
> This fixes also a possible crash when sysrq-t is used.
> Starting with 3.10 sysrq-t calls probe_kernel_read() to
> read details from the kernel workers. As kernel worker are
> completely async pointers may turn NULL while reading them.
>
> Cc: <tj@...nel.org>
> Cc: <stable@...r.kernel.org> # 3.10.x
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
> arch/um/include/shared/os.h | 1 +
> arch/um/kernel/Makefile | 2 +-
> arch/um/kernel/maccess.c | 24 +++++++++++++++++++++
> arch/um/os-Linux/process.c | 52 +++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 78 insertions(+), 1 deletion(-)
> create mode 100644 arch/um/kernel/maccess.c
>
> diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
> index 95feaa4..c70a234 100644
> --- a/arch/um/include/shared/os.h
> +++ b/arch/um/include/shared/os.h
> @@ -200,6 +200,7 @@ extern int os_unmap_memory(void *addr, int len);
> extern int os_drop_memory(void *addr, int length);
> extern int can_drop_memory(void);
> extern void os_flush_stdout(void);
> +extern int os_mincore(void *addr, unsigned long len);
>
> /* execvp.c */
> extern int execvp_noalloc(char *buf, const char *file, char *const argv[]);
> diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
> index babe218..d8b78a0 100644
> --- a/arch/um/kernel/Makefile
> +++ b/arch/um/kernel/Makefile
> @@ -13,7 +13,7 @@ clean-files :=
> obj-y = config.o exec.o exitcode.o irq.o ksyms.o mem.o \
> physmem.o process.o ptrace.o reboot.o sigio.o \
> signal.o smp.o syscall.o sysrq.o time.o tlb.o trap.o \
> - um_arch.o umid.o skas/
> + um_arch.o umid.o maccess.o skas/
>
> obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
> obj-$(CONFIG_GPROF) += gprof_syms.o
> diff --git a/arch/um/kernel/maccess.c b/arch/um/kernel/maccess.c
> new file mode 100644
> index 0000000..214e2e0
> --- /dev/null
> +++ b/arch/um/kernel/maccess.c
> @@ -0,0 +1,24 @@
> +/*
> + * Copyright (C) 2013 Richard Weinberger <richrd@....at>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/uaccess.h>
> +#include <linux/kernel.h>
> +#include <os.h>
> +
> +long probe_kernel_read(void *dst, const void *src, size_t size)
> +{
> + void *psrc = (void *)rounddown((u64)src, PAGE_SIZE);
> +
> + if ((u64)src < PAGE_SIZE || size <= 0)
> + return -EFAULT;
> +
*grrr*, while pressing the send button I realized that it should be s/u64/unsigned long/g.
> + if (os_mincore(psrc, size) <= 0)
> + return -EFAULT;
> +
> + return __probe_kernel_read(dst, src, size);
> +}
> diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
> index b8f34c9..67b9c8f 100644
> --- a/arch/um/os-Linux/process.c
> +++ b/arch/um/os-Linux/process.c
> @@ -4,6 +4,7 @@
> */
>
> #include <stdio.h>
> +#include <stdlib.h>
> #include <unistd.h>
> #include <errno.h>
> #include <signal.h>
> @@ -232,6 +233,57 @@ out:
> return ok;
> }
>
> +static int os_page_mincore(void *addr)
> +{
> + char vec[2];
> + int ret;
> +
> + ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
> + if (ret < 0) {
> + if (errno == ENOMEM || errno == EINVAL)
> + return 0;
> + else
> + return -errno;
> + }
> +
> + return vec[0] & 1;
> +}
> +
> +int os_mincore(void *addr, unsigned long len)
> +{
> + char *vec;
> + int ret, i;
> +
> + if (len <= UM_KERN_PAGE_SIZE)
> + return os_page_mincore(addr);
> +
> + vec = calloc(1, (len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE);
> + if (!vec)
> + return -ENOMEM;
> +
> + ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
> + if (ret < 0) {
> + if (errno == ENOMEM || errno == EINVAL)
> + ret = 0;
> + else
> + ret = -errno;
> +
> + goto out;
> + }
> +
> + for (i = 0; i < ((len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE); i++) {
> + if (!(vec[i] & 1)) {
> + ret = 0;
> + goto out;
> + }
> + }
> +
> + ret = 1;
> +out:
> + free(vec);
> + return ret;
> +}
> +
> void init_new_thread_signals(void)
> {
> set_handler(SIGSEGV);
>
--
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