From a90824b3cb95a1407dc4ea595e739ccf3541d6db Mon Sep 17 00:00:00 2001 From: Edgar Arriaga Date: Mon, 11 Jan 2021 15:19:48 -0800 Subject: [PATCH] FROMLIST: mm/madvise: replace ptrace attach requirement for process_madvise Mot-CRs-fixed: (CR) process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance. Signed-off-by: Suren Baghdasaryan Acked-by: Minchan Kim Acked-by: David Rientjes Link: https://lore.kernel.org/lkml/202101111033.2D03EA97@keescook/T/#u Test: built and flashed kernel Bug: 153444106 Signed-off-by: Edgar Arriaga Change-Id: I3624a8b0697d70f23587c1dcb746ba753c301f45 Reviewed-on: https://gerrit.mot.com/2765787 SME-Granted: SME Approvals Granted SLTApproved: Slta Waiver Tested-by: Jira Key Reviewed-by: Zhangqing Huang Reviewed-by: Huosheng Liao Submit-Approved: Jira Key --- mm/madvise.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/mm/madvise.c b/mm/madvise.c index 72ef91c3a188..739ad2486ebf 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1267,12 +1267,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, goto release_task; } - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; } + /* + * Require CAP_SYS_NICE for influencing process performance. Note that + * only non-destructive hints are currently supported. + */ + if (!capable(CAP_SYS_NICE)) { + ret = -EPERM; + goto release_mm; + } + ret = import_iovec(READ, vec, vlen, ARRAY_SIZE(iovstack), &iov, &iter); if (ret >= 0) { size_t total_len = iov_iter_count(&iter); @@ -1282,6 +1292,8 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, ret = total_len - iov_iter_count(&iter); kfree(iov); } + +release_mm: mmput(mm); release_task: put_task_struct(task);