Hi Suren, On 10/22/22 00:32, Zach OKeefe wrote:
From: Zach O'Keefe <zokeefe@xxxxxxxxxx>
The initial commit of process_madvise(2) to Linux, commit ecb8ac8b1f14
("mm/madvise: introduce process_madvise() syscall: an external memory
hinting API"), relied on PTRACE_MODE_ATTACH_FSCREDS (see ptrace(2)),
but was amended by commit 96cfe2c0fd23 ("mm/madvise: replace ptrace
attach requirement for process_madvise") which replaced this 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).
The initial commit of process_madvise(2) to man-pages project, made
after the second patch, included two errors:
1) CAP_SYS_ADMIN instead of CAP_SYS_NICE
2) PTRACE_MODE_READ_REALCREDS instead of PTRACE_MODE_READ_FSCREDS
Correct this in the man-page for process_madvise(2).
Fixes: a144f458b ("process_madvise.2: Document process_madvise(2)")
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
You added your Reviewed-by tag to v2 of this patch. I guess you'd like to put it in this one too, but since it changed slightly, I'd like you to confirm.
Thanks, Alex
--- man2/process_madvise.2 | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/man2/process_madvise.2 b/man2/process_madvise.2 index 6208206e4..44d3b94e8 100644 --- a/man2/process_madvise.2 +++ b/man2/process_madvise.2 @@ -105,16 +105,20 @@ remote process. No further elements will be processed beyond that point. (See the discussion regarding partial advice in RETURN VALUE.) .PP -Permission to apply advice to another process is governed by a +.\" commit 96cfe2c0fd23ea7c2368d14f769d287e7ae1082e +Starting in Linux 5.12, +permission to apply advice to another process is governed by ptrace access mode -.B PTRACE_MODE_READ_REALCREDS +.B PTRACE_MODE_READ_FSCREDS check (see .BR ptrace (2)); in addition, because of the performance implications of applying the advice, the caller must have the -.B CAP_SYS_ADMIN -capability. +.B CAP_SYS_NICE +capability +(see +.BR capabilities (7)). .SH RETURN VALUE On success, .BR process_madvise () @@ -180,6 +184,15 @@ configuration option. The .BR process_madvise () system call is Linux-specific. +.SH NOTES +When this system call first appeared in Linux 5.10, +permission to apply advice to another process was entirely governed by +ptrace access mode +.B PTRACE_MODE_ATTACH_FSCREDS +check (see +.BR ptrace (2)). +This requirement was relaxed in Linux 5.12 so that the caller didn't require +full control over the target process. .SH SEE ALSO .BR madvise (2), .BR pidfd_open (2),
-- <http://www.alejandro-colomar.es/>
Attachment:
OpenPGP_signature
Description: OpenPGP digital signature
