linux-kernel - [PATCH] usercopy: Do not fail on memory from former init sections

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Message-ID: <YdeHDDAP+TY5wNeT@ls3530>
Date:   Fri, 7 Jan 2022 01:19:24 +0100
From:   Helge Deller <deller@....de>
To:     Linux Kernel <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     linux-parisc@...r.kernel.org
Subject: [PATCH] usercopy: Do not fail on memory from former init sections

On some platforms the memory area between the _stext and the _etext
symbols includes the init sections (parisc and csky). If the init
sections are freed after bootup, the kernel may reuse this memory.

In one test the usercopy checks if the given address is inside the .text
section (from _stext to _etext), and it wrongly fails on the mentioned
platforms if the memory is from the former init section.

Fix this failure by first checking against the init sections before
checking against the _stext/_etext section.

Signed-off-by: Helge Deller <deller@....de>
Fixes: 98400ad75e95 ("parisc: Fix backtrace to always include init funtion names")

diff --git a/mm/usercopy.c b/mm/usercopy.c
index b3de3c4eefba..37a35c6051bc 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -113,6 +113,15 @@ static bool overlaps(const unsigned long ptr, unsigned long n,
 	return true;
 }

+static bool inside_init_area(const unsigned long ptr, unsigned long n,
+		char *start, char *end)
+{
+	unsigned long initlow = (unsigned long) start;
+	unsigned long inithigh = (unsigned long) end;
+
+	return (ptr >= initlow && (ptr + n) < inithigh);
+}
+
 /* Is this address range in the kernel text area? */
 static inline void check_kernel_text_object(const unsigned long ptr,
 					    unsigned long n, bool to_user)
@@ -121,6 +130,12 @@ static inline void check_kernel_text_object(const unsigned long ptr,
 	unsigned long texthigh = (unsigned long)_etext;
 	unsigned long textlow_linear, texthigh_linear;

+	/* Ok if inside the former init sections */
+	if (inside_init_area(ptr, n, __init_begin, __init_end))
+		return;
+	if (inside_init_area(ptr, n, _sinittext, _einittext))
+		return;
+
 	if (overlaps(ptr, n, textlow, texthigh))
 		usercopy_abort("kernel text", NULL, to_user, ptr - textlow, n);