# \[PATCH 1/1\] mm/madvise: replace ptrace attach requirement for process\_madvise - Subsystems: MEMORY MANAGEMENT, MEMORY MAPPING - MADVISE (MEMORY ADVICE), THE REST - Maintainers: Andrew Morton, Liam R. Howlett, Lorenzo Stoakes, David Hildenbrand, Linus Torvalds - List: linux-api - 5 messages, 3 authors - Page: https://ratatoskr.run/linux-api/2021/01/6228145/t ## \[PATCH 1/1\] mm/madvise: replace ptrace attach requirement for process\_madvise - From: Suren Baghdasaryan \ - Date: 2021-01-08 21:00:14 - Message: https://ratatoskr.run/linux-api/2021/01/6228145.md ```text 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 --- mm/madvise.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/madvise.c b/mm/madvise.c index 6a660858784b..c2d600386902 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, 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_task; + } + total_len = iov_iter_count(&iter); while (iov_iter_count(&iter)) { -- 2.30.0.284.gd98b1dd5eaa7-goog ``` ## Re: \[PATCH 1/1\] mm/madvise: replace ptrace attach requirement for process\_madvise - From: Minchan Kim \ - Date: 2021-01-08 22:16:30 - Message: https://ratatoskr.run/linux-api/2021/01/6228222.md ```text On Fri, Jan 08, 2021 at 12:58:57PM -0800, Suren Baghdasaryan wrote: > 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 It sounds logical to me. If security folks don't see any concern and fix below, Acked-by: Minchan Kim > @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > 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_task; mmput? > + } > + > total_len = iov_iter_count(&iter); > > while (iov_iter_count(&iter)) { > -- > 2.30.0.284.gd98b1dd5eaa7-goog > ``` ## Re: \[PATCH 1/1\] mm/madvise: replace ptrace attach requirement for process\_madvise - From: Suren Baghdasaryan \ - Date: 2021-01-08 22:18:30 - Message: https://ratatoskr.run/linux-api/2021/01/6228226.md ```text On Fri, Jan 8, 2021 at 2:15 PM Minchan Kim [ref] wrote: > > On Fri, Jan 08, 2021 at 12:58:57PM -0800, Suren Baghdasaryan wrote: > > 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 > > It sounds logical to me. > If security folks don't see any concern and fix below, > > Acked-by: Minchan Kim > > > @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > > 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_task; > > mmput? Ouch! Thanks for pointing it out! Will include in the next respin. > > > + } > > + > > total_len = iov_iter_count(&iter); > > > > while (iov_iter_count(&iter)) { > > -- > > 2.30.0.284.gd98b1dd5eaa7-goog > > > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. > ``` ## Re: \[PATCH 1/1\] mm/madvise: replace ptrace attach requirement for process\_madvise - From: David Rientjes \ - Date: 2021-01-09 01:03:14 - Message: https://ratatoskr.run/linux-api/2021/01/6228326.md ```text On Fri, 8 Jan 2021, Suren Baghdasaryan wrote: > > > @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > > > 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_task; > > > > mmput? > > Ouch! Thanks for pointing it out! Will include in the next respin. > With the fix, feel free to add: Acked-by: David Rientjes [ref] Thanks Suren! ``` ## Re: \[PATCH 1/1\] mm/madvise: replace ptrace attach requirement for process\_madvise - From: Suren Baghdasaryan \ - Date: 2021-01-09 02:20:23 - Message: https://ratatoskr.run/linux-api/2021/01/6228366.md ```text On Fri, Jan 8, 2021 at 5:02 PM David Rientjes [ref] wrote: > > On Fri, 8 Jan 2021, Suren Baghdasaryan wrote: > > > > > @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > > > > 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_task; > > > > > > mmput? > > > > Ouch! Thanks for pointing it out! Will include in the next respin. > > > > With the fix, feel free to add: > > Acked-by: David Rientjes [ref] Thanks! Will post a new version with the fix on Monday. > > Thanks Suren! ```