Messages in this thread Patches in this message | | | Date | Tue, 11 Sep 2018 15:30:57 +0800 | From | Baoquan He <> | Subject | Re: [PATCH v2 2/3] x86/mm/KASLR: Calculate the actual size of vmemmap region |
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On 09/10/18 at 08:11am, Ingo Molnar wrote: > > * Baoquan He <bhe@redhat.com> wrote: > > > @@ -108,6 +109,14 @@ void __init kernel_randomize_memory(void) > > if (memory_tb < kaslr_regions[0].size_tb) > > kaslr_regions[0].size_tb = memory_tb; > > > > + /* > > + * Calculate how many TB vmemmap region needs, and align to > > + * 1TB boundary. > > + * */ > > Yeah, so that's not the standard comment style ...
Sorry for this, Will change. Thanks.
About clean up you suggested, I have made two patches and paste them at below. Please help check if it's OK. Thanks a lot.
> So I get the part where the 'base' pointer is essentially pointers to various global variables > used by the MM to get the virtual base address of the kernel, vmalloc and vmemmap areas from, > which base addresses can thus be modified by the very early KASLR code to dynamically shape the > virtual memory layout of these kernel memory areas on a per bootup basis. > > (BTW., that would be a great piece of information to add for the uninitiated. It's not like > it's obvious!) > > But what does 'size_tb' do? Nothing explains it and your patch doesn't make it clearer either. > Also, get_padding() looks like an unnecessary layer of obfuscation:
Yes, I agree. Have made an patch according to your suggestion, paste it here:
From c74b1e49eaa0e00335adbbb7e2d5df6d60518d4f Mon Sep 17 00:00:00 2001 From: Baoquan He <bhe@redhat.com> Date: Tue, 11 Sep 2018 14:34:26 +0800 Subject: [PATCH] x86/mm/KASLR: Add code comments to explain fields of struct kaslr_memory_region
Signed-off-by: Baoquan He <bhe@redhat.com> Suggested-by: Ingo Molnar <mingo@kernel.org>
--- arch/x86/mm/kaslr.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 91053cee7648..402984d8d729 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -41,9 +41,21 @@ static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE; /* - * Memory regions randomized by KASLR (except modules that use a separate logic - * earlier during boot). The list is ordered based on virtual addresses. This - * order is kept after randomization. + * Memory regions randomized by KASLR (except modules that use a separate + * logic earlier during boot). Currently they are the physical memory + * mapping, vmalloc and vmemmap regions, are ordered based on virtual + * addresses. The order is kept after randomization. + * + * @base: points to various global variables used by the MM to get the + * virtual base address of the above regions, which base addresses can + * thus be modified by the very early KASLR code to dynamically shape + * the virtual memory layout of these kernel memory regions on a per + * bootup basis. + * + * @size_tb: size in TB of each memory region. Thereinto, the size of + * the physical memory mapping region is variable, calculated according + * to the actual size of system RAM in order to save more space for + * randomization. The rest are fixed values related to paging mode. */ static __initdata struct kaslr_memory_region { unsigned long *base; > /* Get size in bytes used by the memory region */ > static inline unsigned long get_padding(struct kaslr_memory_region *region) > { > return (region->size_tb << TB_SHIFT); > }
Yes, we can open code get_padding() as the following patch.
From e4cababd630af06085cb79a0bae9c00acd5272c0 Mon Sep 17 00:00:00 2001 From: Baoquan He <bhe@redhat.com> Date: Tue, 11 Sep 2018 14:39:38 +0800 Subject: [PATCH] x86/mm/KASLR: Open code unnecessary function get_padding
It's used only twice and we do bit shifts in the parent function anyway so it's not like it's hiding some uninteresting detail.
Signed-off-by: Baoquan He <bhe@redhat.com> Suggested-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/mm/kaslr.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 9774b6e39f63..91053cee7648 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -54,12 +54,6 @@ static __initdata struct kaslr_memory_region { { &vmemmap_base, 0 }, }; -/* Get size in bytes used by the memory region */ -static inline unsigned long get_padding(struct kaslr_memory_region *region) -{ - return (region->size_tb << TB_SHIFT); -} - /* * Apply no randomization if KASLR was disabled at boot or if KASAN * is enabled. KASAN shadow mappings rely on regions being PGD aligned. @@ -120,7 +114,7 @@ void __init kernel_randomize_memory(void) /* Calculate entropy available between regions */ remain_entropy = vaddr_end - vaddr_start; for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) - remain_entropy -= get_padding(&kaslr_regions[i]); + remain_entropy -= kaslr_regions[i].size_tb << TB_SHIFT; prandom_seed_state(&rand_state, kaslr_get_random_long("Memory")); @@ -144,7 +138,7 @@ void __init kernel_randomize_memory(void) * Jump the region and add a minimum padding based on * randomization alignment. */ - vaddr += get_padding(&kaslr_regions[i]); + vaddr += kaslr_regions[i].size_tb << TB_SHIFT; if (pgtable_l5_enabled()) vaddr = round_up(vaddr + 1, P4D_SIZE); else -- 2.13.6
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