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x86: Clear .brk area at early boot

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[ Upstream commit 38fa5479b4 ]

The .brk section has the same properties as .bss: it is an alloc-only
section and should be cleared before being used.

Not doing so is especially a problem for Xen PV guests, as the
hypervisor will validate page tables (check for writable page tables
and hypervisor private bits) before accepting them to be used.

Make sure .brk is initially zero by letting clear_bss() clear the brk
area, too.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220630071441.28576-3-jgross@suse.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Juergen Gross 2022-06-30 09:14:40 +02:00 committed by Greg Kroah-Hartman
parent ee1da3d596
commit 26bb7afc02
1 changed files with 2 additions and 0 deletions
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arch/x86/kernel/head64.c
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@ -418,6 +418,8 @@ static void __init clear_bss(void)
{
memset(__bss_start, 0,
(unsigned long) __bss_stop - (unsigned long) __bss_start);
memset(__brk_base, 0,
(unsigned long) __brk_limit - (unsigned long) __brk_base);
}
static unsigned long get_cmd_line_ptr(void)