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[34.82.4.56]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-20d1804c050sm34102105ad.216.2024.10.16.17.51.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Oct 2024 17:51:10 -0700 (PDT) From: jeffxu@chromium.org To: akpm@linux-foundation.org, keescook@chromium.org, torvalds@linux-foundation.org, usama.anjum@collabora.com, corbet@lwn.net, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com Cc: jeffxu@google.com, jorgelo@chromium.org, groeck@chromium.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, jannh@google.com, sroettger@google.com, pedro.falcato@gmail.com, linux-hardening@vger.kernel.org, willy@infradead.org, gregkh@linuxfoundation.org, deraadt@openbsd.org, surenb@google.com, merimus@google.com, rdunlap@infradead.org, Jeff Xu , stable@vger.kernel.org Subject: [PATCH v1 1/2] mseal: Two fixes for madvise(MADV_DONTNEED) when sealed Date: Thu, 17 Oct 2024 00:51:04 +0000 Message-ID: <20241017005105.3047458-2-jeffxu@chromium.org> X-Mailer: git-send-email 2.47.0.rc1.288.g06298d1525-goog In-Reply-To: <20241017005105.3047458-1-jeffxu@chromium.org> References: <20241017005105.3047458-1-jeffxu@chromium.org> MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 8B3A7C000C X-Stat-Signature: m17ksensdk58pdeq6wonmapp3yaj3gfi X-HE-Tag: 1729126269-290122 X-HE-Meta: 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 4jL6rILe ZOfN/AkWM5Ai4FrTNkAN71eCwdoWvoJzqj6nObVkbKqz+yvXMUf1YDGFZZaNJZs3WxREsZwQ159KNMmr2+awQTU95y7yovtX3BK0Ahf3g2z8ktDeyv37V5B1PRtf2dfqS17hrFe7HPQIPd9GQC71GSbKbHkbpUdf15mLBr/cLNFOESHWHKi3e2CsnaHX3c2ApKsYRjTkMvqBBWq11zRwsv4m5dJpwFifBOz6oiCC3NFN3K++LxJ1XECx6PGRn6yxq0nJhPccgFaPgINb+2/Hvbkr1H1TTCfYz602XfpqRzTuPovCTlLRG5VTuK3s3RjQAdlRCQpNt+tWMtJU+mEdaDbaYYqXRQLZuwOtlWkufkFu1oe0yy3r730LWv/lJFqTHZMWod39e0xbll5inJNmLCLmtp/qQ+DnWVZxYzNfOFwo9ESA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Jeff Xu Two fixes for madvise(MADV_DONTNEED) when sealed. For PROT_NONE mappings, the previous blocking of madvise(MADV_DONTNEED) is unnecessary. As PROT_NONE already prohibits memory access, madvise(MADV_DONTNEED) should be allowed to proceed in order to free the page. For file-backed, private, read-only memory mappings, we previously did not block the madvise(MADV_DONTNEED). This was based on the assumption that the memory's content, being file-backed, could be retrieved from the file if accessed again. However, this assumption failed to consider scenarios where a mapping is initially created as read-write, modified, and subsequently changed to read-only. The newly introduced VM_WASWRITE flag addresses this oversight. Reported-by: Pedro Falcato Link:https://lore.kernel.org/all/CABi2SkW2XzuZ2-TunWOVzTEX1qc29LhjfNQ3hD4Nym8U-_f+ug@mail.gmail.com/ Fixes: 8be7258aad44 ("mseal: add mseal syscall") Cc: # 6.11.y: 4d1b3416659b: mm: move can_modify_vma to mm/vma.h Cc: # 6.11.y: 4a2dd02b0916: mm/mprotect: replace can_modify_mm with can_modify_vma Cc: # 6.11.y: 23c57d1fa2b9: mseal: replace can_modify_mm_madv with a vma variant Cc: # 6.11.y Signed-off-by: Jeff Xu Signed-off-by: Pedro Falcato --- include/linux/mm.h | 2 ++ mm/mprotect.c | 3 +++ mm/mseal.c | 42 ++++++++++++++++++++++++++++++++++++------ 3 files changed, 41 insertions(+), 6 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 4c32003c8404..b402eca2565a 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -430,6 +430,8 @@ extern unsigned int kobjsize(const void *objp); #ifdef CONFIG_64BIT /* VM is sealed, in vm_flags */ #define VM_SEALED _BITUL(63) +/* VM was writable */ +#define VM_WASWRITE _BITUL(62) #endif /* Bits set in the VMA until the stack is in its final location */ diff --git a/mm/mprotect.c b/mm/mprotect.c index 0c5d6d06107d..6397135ca526 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -821,6 +821,9 @@ static int do_mprotect_pkey(unsigned long start, size_t len, break; } + if ((vma->vm_flags & VM_WRITE) && !(newflags & VM_WRITE)) + newflags |= VM_WASWRITE; + error = security_file_mprotect(vma, reqprot, prot); if (error) break; diff --git a/mm/mseal.c b/mm/mseal.c index ece977bd21e1..28f28487be17 100644 --- a/mm/mseal.c +++ b/mm/mseal.c @@ -36,12 +36,8 @@ static bool is_madv_discard(int behavior) return false; } -static bool is_ro_anon(struct vm_area_struct *vma) +static bool anon_is_ro(struct vm_area_struct *vma) { - /* check anonymous mapping. */ - if (vma->vm_file || vma->vm_flags & VM_SHARED) - return false; - /* * check for non-writable: * PROT=RO or PKRU is not writeable. @@ -53,6 +49,22 @@ static bool is_ro_anon(struct vm_area_struct *vma) return false; } +static bool vma_is_prot_none(struct vm_area_struct *vma) +{ + if ((vma->vm_flags & VM_ACCESS_FLAGS) == VM_NONE) + return true; + + return false; +} + +static bool vma_was_writable_turn_readonly(struct vm_area_struct *vma) +{ + if (!(vma->vm_flags & VM_WRITE) && vma->vm_flags & VM_WASWRITE) + return true; + + return false; +} + /* * Check if a vma is allowed to be modified by madvise. */ @@ -61,7 +73,25 @@ bool can_modify_vma_madv(struct vm_area_struct *vma, int behavior) if (!is_madv_discard(behavior)) return true; - if (unlikely(!can_modify_vma(vma) && is_ro_anon(vma))) + /* not sealed */ + if (likely(can_modify_vma(vma))) + return true; + + /* PROT_NONE mapping */ + if (vma_is_prot_none(vma)) + return true; + + /* file-backed private mapping */ + if (vma->vm_file) { + /* read-only but was writeable */ + if (vma_was_writable_turn_readonly(vma)) + return false; + + return true; + } + + /* anonymous mapping is read-only */ + if (anon_is_ro(vma)) return false; /* Allow by default. */