linux-kernel - [PATCH 5.4 12/92] Revert "parisc: Fix backtrace to always include init funtion names"

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Message-Id: <20211129181707.833782456@linuxfoundation.org>
Date:   Mon, 29 Nov 2021 19:17:41 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Helge Deller <deller@....de>,
        stable@...nel.org
Subject: [PATCH 5.4 12/92] Revert "parisc: Fix backtrace to always include init funtion names"

From: Helge Deller <deller@....de>

commit 98400ad75e95860e9a10ec78b0b90ab66184a2ce upstream.

This reverts commit 279917e27edc293eb645a25428c6ab3f3bca3f86.

With the CONFIG_HARDENED_USERCOPY option enabled, this patch triggers
kernel bugs at runtime:

  usercopy: Kernel memory overwrite attempt detected to kernel text (offset 2084839, size 6)!
  kernel BUG at mm/usercopy.c:99!
 Backtrace:
  IAOQ[0]: usercopy_abort+0xc4/0xe8
  [<00000000406ed1c8>] __check_object_size+0x174/0x238
  [<00000000407086d4>] copy_strings.isra.0+0x3e8/0x708
  [<0000000040709a20>] do_execveat_common.isra.0+0x1bc/0x328
  [<000000004070b760>] compat_sys_execve+0x7c/0xb8
  [<0000000040303eb8>] syscall_exit+0x0/0x14

The problem is, that we have an init section of at least 2MB size which
starts at _stext and is freed after bootup.

If then later some kernel data is (temporarily) stored in this free
memory, check_kernel_text_object() will trigger a bug since the data
appears to be inside the kernel text (>=_stext) area:
        if (overlaps(ptr, len, _stext, _etext))
                usercopy_abort("kernel text");

Signed-off-by: Helge Deller <deller@....de>
Cc: stable@...nel.org # 5.4+
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/parisc/kernel/vmlinux.lds.S |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/arch/parisc/kernel/vmlinux.lds.S
+++ b/arch/parisc/kernel/vmlinux.lds.S
@@ -56,8 +56,6 @@ SECTIONS
 {
 	. = KERNEL_BINARY_TEXT_START;

-	_stext = .;	/* start of kernel text, includes init code & data */
-
 	__init_begin = .;
 	HEAD_TEXT_SECTION
 	MLONGCALL_DISCARD(INIT_TEXT_SECTION(8))
@@ -81,6 +79,7 @@ SECTIONS
 	/* freed after init ends here */

 	_text = .;		/* Text and read-only data */
+	_stext = .;
 	MLONGCALL_KEEP(INIT_TEXT_SECTION(8))
 	.text ALIGN(PAGE_SIZE) : {
 		TEXT_TEXT