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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Naresh Kamboju <naresh.kamboju@linaro.org>,
        Song Liu <songliubraving@fb.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.20 065/183] bpf: fix panic in stack_map_get_build_id() on i386 and arm32
Date:   Mon, 25 Feb 2019 22:10:38 +0100
Message-Id: <20190225195105.488099969@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit beaf3d1901f4ea46fbd5c9d857227d99751de469 ]

As Naresh reported, test_stacktrace_build_id() causes panic on i386 and
arm32 systems. This is caused by page_address() returns NULL in certain
cases.

This patch fixes this error by using kmap_atomic/kunmap_atomic instead
of page_address.

Fixes: 615755a77b24 (" bpf: extend stackmap to save binary_build_id+offset instead of address")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/stackmap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 90daf285de032..d9e2483669d0b 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -260,7 +260,7 @@ static int stack_map_get_build_id(struct vm_area_struct *vma,
 		return -EFAULT;	/* page not mapped */
 
 	ret = -EINVAL;
-	page_addr = page_address(page);
+	page_addr = kmap_atomic(page);
 	ehdr = (Elf32_Ehdr *)page_addr;
 
 	/* compare magic x7f "ELF" */
@@ -276,6 +276,7 @@ static int stack_map_get_build_id(struct vm_area_struct *vma,
 	else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
 		ret = stack_map_get_build_id_64(page_addr, build_id);
 out:
+	kunmap_atomic(page_addr);
 	put_page(page);
 	return ret;
 }
-- 
2.19.1