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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 , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, 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 , Mark Brown X-Mailer: b4 0.15-dev-99b12 X-Developer-Signature: v=1; a=openpgp-sha256; l=2551; i=broonie@kernel.org; h=from:subject:message-id; bh=6l7d6i2Hr/t16H3e0PM6ntsqOX0xtByvRrAFpx2RPdc=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBm2JLp8oAy9lYwTYiPgligR57zoDd7L+at5nOq93BI UyufcpKJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZtiS6QAKCRAk1otyXVSH0OADB/ 0ch6Ppo1cUyP74KOdaZaA30djq+AGYfXlBTOUWViXVC9fGK3bpaqsBB0Cfo7Fu6OsGVc21oO0/yUH1 YrAVYn6NPOHjgywpcI1TnkgqUaxfBOur+h4alPeKfO22P8IGuFmDQWUyfu/9w5PhhvsetXQF8HjY3+ VA0L3qH2XKq516PsycNgfFI7aYDz9EL8tCzzuTsMp8jhgeTHcVNNcxzbWDDBDU5qQBsU5P9IwQfOAx OuEH/w/+Xqho79dLxhqBNChGpSjBv7foaNTf0PLA9gi1zV9CAxhWJ6oVaByM60hUmP9mC93njCQXlg DUm9swJvc4113Ub/xAIxFMCk0q1OCk X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB As covered in the commit log for c44357c2e76b ("x86/mm: care about shadow stack guard gap during placement") our current mmap() implementation does not take care to ensure that a new mapping isn't placed with existing mappings inside it's own guard gaps. 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. x86 uses a single page guard, this is also sufficient for arm64 where we either do single word pops and pushes or unconstrained writes. Architectures which do not have this feature will define VM_SHADOW_STACK to VM_NONE and hence be unaffected. Suggested-by: Rick Edgecombe Acked-by: Lorenzo Stoakes Signed-off-by: Mark Brown --- mm/mmap.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/mmap.c b/mm/mmap.c index b06ba847c96e..050c5ae2f80f 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1753,6 +1753,18 @@ static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info) return gap; } +/* + * Determine if the allocation needs to ensure that there is no + * existing mapping within it's guard gaps, for use as start_gap. + */ +static inline unsigned long stack_guard_placement(vm_flags_t vm_flags) +{ + if (vm_flags & VM_SHADOW_STACK) + return PAGE_SIZE; + + return 0; +} + /* * Search for an unmapped address range. * @@ -1814,6 +1826,7 @@ 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 +1876,7 @@ 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); /*