[PATCH] riscv: mm: Fix W+X mappings at boot

Jisheng Zhang
2021-05-16T09:06:47Z

From: Jisheng Zhang <jszhang@kernel.org>

When the kernel mapping was moved the last 2GB of the address space,
(__va(PFN_PHYS(max_low_pfn))) is much smaller than the .data section
start address, the last set_memory_nx() in protect_kernel_text_data()
will fail, thus the .data section is still mapped as W+X. This results
in below W+X mapping waring at boot. Fix it by passing the correct
.data section page num to the set_memory_nx().

[ 0.396516] ------------[ cut here ]------------
[ 0.396889] riscv/mm: Found insecure W+X mapping at address (____ptrval____)/0xffffffff80c00000
[ 0.398347] WARNING: CPU: 0 PID: 1 at arch/riscv/mm/ptdump.c:258 note_page+0x244/0x24a
[ 0.398964] Modules linked in:
[ 0.399459] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc1+ #14
[ 0.400003] Hardware name: riscv-virtio,qemu (DT)
[ 0.400591] epc : note_page+0x244/0x24a
[ 0.401368] ra : note_page+0x244/0x24a
[ 0.401772] epc : ffffffff80007c86 ra : ffffffff80007c86 sp : ffffffe000e7bc30
[ 0.402304] gp : ffffffff80caae88 tp : ffffffe000e70000 t0 : ffffffff80cb80cf
[ 0.402800] t1 : ffffffff80cb80c0 t2 : 0000000000000000 s0 : ffffffe000e7bc80
[ 0.403310] s1 : ffffffe000e7bde8 a0 : 0000000000000053 a1 : ffffffff80c83ff0
[ 0.403805] a2 : 0000000000000010 a3 : 0000000000000000 a4 : 6c7e7a5137233100
[ 0.404298] a5 : 6c7e7a5137233100 a6 : 0000000000000030 a7 : ffffffffffffffff
[ 0.404849] s2 : ffffffff80e00000 s3 : 0000000040000000 s4 : 0000000000000000
[ 0.405393] s5 : 0000000000000000 s6 : 0000000000000003 s7 : ffffffe000e7bd48
[ 0.405935] s8 : ffffffff81000000 s9 : ffffffffc0000000 s10: ffffffe000e7bd48
[ 0.406476] s11: 0000000000001000 t3 : 0000000000000072 t4 : ffffffffffffffff
[ 0.407016] t5 : 0000000000000002 t6 : ffffffe000e7b978
[ 0.407435] status: 0000000000000120 badaddr: 0000000000000000 cause: 0000000000000003
[ 0.408052] Call Trace:
[ 0.408343] [<ffffffff80007c86>] note_page+0x244/0x24a
[ 0.408855] [<ffffffff8010c5a6>] ptdump_hole+0x14/0x1e
[ 0.409263] [<ffffffff800f65c6>] walk_pgd_range+0x2a0/0x376
[ 0.409690] [<ffffffff800f6828>] walk_page_range_novma+0x4e/0x6e
[ 0.410146] [<ffffffff8010c5f8>] ptdump_walk_pgd+0x48/0x78
[ 0.410570] [<ffffffff80007d66>] ptdump_check_wx+0xb4/0xf8
[ 0.410990] [<ffffffff80006738>] mark_rodata_ro+0x26/0x2e
[ 0.411407] [<ffffffff8031961e>] kernel_init+0x44/0x108
[ 0.411814] [<ffffffff80002312>] ret_from_exception+0x0/0xc
[ 0.412309] ---[ end trace 7ec3459f2547ea83 ]---
[ 0.413141] Checked W+X mappings: failed, 512 W+X pages found

Fixes: 2bfc6cd81bd17e43 ("riscv: Move kernel mapping outside of linear mapping")
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
arch/riscv/mm/init.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 4faf8bd157ea..4c4c92ce0bb8 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -746,14 +746,18 @@ void __init protect_kernel_text_data(void)
unsigned long init_data_start = (unsigned long)__init_data_begin;
unsigned long rodata_start = (unsigned long)__start_rodata;
unsigned long data_start = (unsigned long)_data;
- unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
+#if defined(CONFIG_64BIT) && defined(CONFIG_MMU)
+ unsigned long end_va = kernel_virt_addr + load_sz;
+#else
+ unsigned long end_va = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
+#endif

set_memory_ro(text_start, (init_text_start - text_start) >> PAGE_SHIFT);
set_memory_ro(init_text_start, (init_data_start - init_text_start) >> PAGE_SHIFT);
set_memory_nx(init_data_start, (rodata_start - init_data_start) >> PAGE_SHIFT);
/* rodata section is marked readonly in mark_rodata_ro */
set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
- set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
+ set_memory_nx(data_start, (end_va - data_start) >> PAGE_SHIFT);
}

void mark_rodata_ro(void)
--
2.31.0