From: Baoquan He bhe@redhat.com
[ Upstream commit ec3937107ab43f3e8b2bc9dad95710043c462ff7 ]
kernel_randomize_memory() uses __PHYSICAL_MASK_SHIFT to calculate the maximum amount of system RAM supported. The size of the direct mapping section is obtained from the smaller one of the below two values:
(actual system RAM size + padding size) vs (max system RAM size supported)
This calculation is wrong since commit
b83ce5ee9147 ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52").
In it, __PHYSICAL_MASK_SHIFT was changed to be 52, regardless of whether the kernel is using 4-level or 5-level page tables. Thus, it will always use 4 PB as the maximum amount of system RAM, even in 4-level paging mode where it should actually be 64 TB.
Thus, the size of the direct mapping section will always be the sum of the actual system RAM size plus the padding size.
Even when the amount of system RAM is 64 TB, the following layout will still be used. Obviously KALSR will be weakened significantly.
|____|_______actual RAM_______|_padding_|______the rest_______| 0 64TB ~120TB
Instead, it should be like this:
|____|_______actual RAM_______|_________the rest______________| 0 64TB ~120TB
The size of padding region is controlled by CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING, which is 10 TB by default.
The above issue only exists when CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING is set to a non-zero value, which is the case when CONFIG_MEMORY_HOTPLUG is enabled. Otherwise, using __PHYSICAL_MASK_SHIFT doesn't affect KASLR.
Fix it by replacing __PHYSICAL_MASK_SHIFT with MAX_PHYSMEM_BITS.
[ bp: Massage commit message. ]
Fixes: b83ce5ee9147 ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52") Signed-off-by: Baoquan He bhe@redhat.com Signed-off-by: Borislav Petkov bp@suse.de Reviewed-by: Thomas Garnier thgarnie@google.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Andy Lutomirski luto@kernel.org Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Ingo Molnar mingo@kernel.org Cc: Kees Cook keescook@chromium.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: frank.ramsay@hpe.com Cc: herbert@gondor.apana.org.au Cc: kirill@shutemov.name Cc: mike.travis@hpe.com Cc: thgarnie@google.com Cc: x86-ml x86@kernel.org Cc: yamada.masahiro@socionext.com Link: https://lkml.kernel.org/r/20190417083536.GE7065@MiWiFi-R3L-srv Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/mm/kaslr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 61db77b0eda9..0988971069c9 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -93,7 +93,7 @@ void __init kernel_randomize_memory(void) if (!kaslr_memory_enabled()) return;
- kaslr_regions[0].size_tb = 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT); + kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT); kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
/*