6.16-stable review patch. If anyone has any objections, please let me know.
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From: Heiko Carstens hca@linux.ibm.com
[ Upstream commit 93f616ff870a1fb7e84d472cad0af651b18f9f87 ]
Since the identity mapping is pinned to address zero the lowcore is always also mapped to address zero, this happens regardless of the relocate_lowcore command line option. If the option is specified the lowcore is mapped twice, instead of only once.
This means that NULL pointer accesses will succeed instead of causing an exception (low address protection still applies, but covers only parts). To fix this never map the first two pages of physical memory with the identity mapping.
Fixes: 32db401965f1 ("s390/mm: Pin identity mapping base to zero") Reviewed-by: Alexander Gordeev agordeev@linux.ibm.com Signed-off-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Alexander Gordeev agordeev@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/s390/boot/vmem.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/s390/boot/vmem.c b/arch/s390/boot/vmem.c index 1d073acd05a7..cea3de4dce8c 100644 --- a/arch/s390/boot/vmem.c +++ b/arch/s390/boot/vmem.c @@ -530,6 +530,9 @@ void setup_vmem(unsigned long kernel_start, unsigned long kernel_end, unsigned l lowcore_address + sizeof(struct lowcore), POPULATE_LOWCORE); for_each_physmem_usable_range(i, &start, &end) { + /* Do not map lowcore with identity mapping */ + if (!start) + start = sizeof(struct lowcore); pgtable_populate((unsigned long)__identity_va(start), (unsigned long)__identity_va(end), POPULATE_IDENTITY);