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Howlett" To: Mark Brown Cc: Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Russell King , Guo Ren , Huacai Chen , WANG Xuerui , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , "David S. Miller" , Andreas Larsson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Chris Zankel , Max Filippov , Andrew Morton , Vlastimil Babka , Lorenzo Stoakes , Catalin Marinas , Will Deacon , Deepak Gupta , linux-arm-kernel@lists.infradead.org, linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-csky@vger.kernel.org, loongarch@lists.linux.dev, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, Rick Edgecombe Subject: Re: [PATCH 3/3] mm: Care about shadow stack guard gap when getting an unmapped area Message-ID: Mail-Followup-To: "Liam R. Howlett" , Mark Brown , Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Russell King , Guo Ren , Huacai Chen , WANG Xuerui , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , "David S. Miller" , Andreas Larsson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Chris Zankel , Max Filippov , Andrew Morton , Vlastimil Babka , Lorenzo Stoakes , Catalin Marinas , Will Deacon , Deepak Gupta , linux-arm-kernel@lists.infradead.org, linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-csky@vger.kernel.org, loongarch@lists.linux.dev, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, Rick Edgecombe References: <20240902-mm-generic-shadow-stack-guard-v1-0-9acda38b3dd3@kernel.org> <20240902-mm-generic-shadow-stack-guard-v1-3-9acda38b3dd3@kernel.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240902-mm-generic-shadow-stack-guard-v1-3-9acda38b3dd3@kernel.org> User-Agent: NeoMutt/20240425 X-ClientProxiedBy: YT4PR01CA0206.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:ad::16) To LV8PR10MB7943.namprd10.prod.outlook.com (2603:10b6:408:1f9::22) 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1725392520-571777 X-HE-Meta: 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 cHGTab51 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This is particularly important for > shadow stacks since if two shadow stacks end up getting placed adjacent to > each other then they can overflow into each other which weakens the > protection offered by the feature. > > On x86 there is a custom arch_get_unmapped_area() which was updated by the > above commit to cover this case by specifying a start_gap for allocations > with VM_SHADOW_STACK. Both arm64 and RISC-V have equivalent features and > use the generic implementation of arch_get_unmapped_area() so let's make > the equivalent change there so they also don't get shadow stack pages > placed without guard pages. > > Architectures which do not have this feature will define VM_SHADOW_STACK > to VM_NONE and hence be unaffected. > > Suggested-by: Rick Edgecombe > Signed-off-by: Mark Brown > --- > mm/mmap.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index b06ba847c96e..902c482b6084 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1753,6 +1753,14 @@ static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info) > return gap; > } > > +static inline unsigned long stack_guard_placement(vm_flags_t vm_flags) > +{ > + if (vm_flags & VM_SHADOW_STACK) > + return PAGE_SIZE; Is PAGE_SIZE is enough? > + > + return 0; > +} > + > /* > * Search for an unmapped address range. > * > @@ -1814,6 +1822,7 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr, > info.length = len; > info.low_limit = mm->mmap_base; > info.high_limit = mmap_end; > + info.start_gap = stack_guard_placement(vm_flags); > return vm_unmapped_area(&info); > } > > @@ -1863,6 +1872,7 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr, > info.length = len; > info.low_limit = PAGE_SIZE; > info.high_limit = arch_get_mmap_base(addr, mm->mmap_base); > + info.start_gap = stack_guard_placement(vm_flags); > addr = vm_unmapped_area(&info); > > /* > > -- > 2.39.2 >