[PATCH] uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()

[PATCH] uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()

[Oleg Nesterov]

Sorry for double-posting, but it seems that this patch didn't reach
lkml. Let me resend it just on case. Plus another patch in reply, on
top of this change.

-------------------------------------------------------------------------------
Subject: [PATCH] uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()

copy_insn() fails with -EIO if ->readpage == NULL, but this error
is not propagated unless uprobe_register() path finds ->mm which
already mmaps this file. In this case (say) "perf record" does not
actually install the probe, but the user can't know about this.

Move this check into uprobe_register() so that this problem can be
detected earlier and reported to user.

Note: this is still not perfect,

	- copy_insn() and arch_uprobe_analyze_insn() should be called
	  by uprobe_register() but this is not simple, we need vm_file
	  for read_mapping_page() (although perhaps we can pass NULL),
	  and we need ->mm for is_64bit_mm() (although this logic is
	  broken anyway).

	- uprobe_register() should be called by create_trace_uprobe(),
	  not by probe_event_enable(), so that an error can be detected
	  at "perf probe -x" time. This also needs more changes in the
	  core uprobe code, uprobe register/unregister interface was
	  poorly designed from the very beginning.

Reported-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/events/uprobes.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 3b02c72..c56b13e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -536,9 +536,6 @@ static int __copy_insn(struct address_space *mapping, struct file *filp,
 			void *insn, int nbytes, loff_t offset)
 {
 	struct page *page;
-
-	if (!mapping->a_ops->readpage)
-		return -EIO;
 	/*
 	 * Ensure that the page that has the original instruction is
 	 * populated and in page-cache.
@@ -879,6 +876,9 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
 	if (!uc->handler && !uc->ret_handler)
 		return -EINVAL;
 
+	/* copy_insn()->read_mapping_page() needs ->readpage() */
+	if (!inode->i_mapping->a_ops->readpage)
+		return -EIO;
 	/* Racy, just to catch the obvious mistakes */
 	if (offset > i_size_read(inode))
 		return -EINVAL;
-- 
1.5.5.1

[PATCH] uprobes: Teach copy_insn() to support tmpfs

[Oleg Nesterov]

tmpfs is widely used but as Denys reports shmem_aops doesn't have
->readpage() and thus you can't probe a binary on this filesystem.

As Hugh suggested we can use shmem_read_mapping_page() in this case,
just we need to check shmem_mapping() if ->readpage == NULL.

Reported-by: Denys Vlasenko <dvlasenk@redhat.com>
Suggested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/events/uprobes.c |   15 ++++++++++-----
 1 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c56b13e..6bfb671 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -36,6 +36,7 @@
 #include "../../mm/internal.h"	/* munlock_vma_page */
 #include <linux/percpu-rwsem.h>
 #include <linux/task_work.h>
+#include <linux/shmem_fs.h>
 
 #include <linux/uprobes.h>
 
@@ -537,10 +538,14 @@ static int __copy_insn(struct address_space *mapping, struct file *filp,
 {
 	struct page *page;
 	/*
-	 * Ensure that the page that has the original instruction is
-	 * populated and in page-cache.
+	 * Ensure that the page that has the original instruction is populated
+	 * and in page-cache. If ->readpage == NULL it must be shmem_mapping(),
+	 * see uprobe_register().
 	 */
-	page = read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT, filp);
+	if (mapping->a_ops->readpage)
+		page = read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT, filp);
+	else
+		page = shmem_read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT);
 	if (IS_ERR(page))
 		return PTR_ERR(page);
 
@@ -876,8 +881,8 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
 	if (!uc->handler && !uc->ret_handler)
 		return -EINVAL;
 
-	/* copy_insn()->read_mapping_page() needs ->readpage() */
-	if (!inode->i_mapping->a_ops->readpage)
+	/* copy_insn() uses read_mapping_page() or shmem_read_mapping_page() */
+	if (!inode->i_mapping->a_ops->readpage && !shmem_mapping(inode->i_mapping))
 		return -EIO;
 	/* Racy, just to catch the obvious mistakes */
 	if (offset > i_size_read(inode))
-- 
1.5.5.1

Re: [PATCH] uprobes: Teach copy_insn() to support tmpfs

[Srikar Dronamraju]

* Oleg Nesterov <oleg@redhat.com> [2014-05-19 20:41:36]:

> tmpfs is widely used but as Denys reports shmem_aops doesn't have
> ->readpage() and thus you can't probe a binary on this filesystem.
> 
> As Hugh suggested we can use shmem_read_mapping_page() in this case,
> just we need to check shmem_mapping() if ->readpage == NULL.
> 
> Reported-by: Denys Vlasenko <dvlasenk@redhat.com>
> Suggested-by: Hugh Dickins <hughd@google.com>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

-- 
Thanks and Regards
Srikar Dronamraju

[tip:perf/core] uprobes: Teach copy_insn() to support tmpfs

[tip-bot for Oleg Nesterov]

Commit-ID:  40814f6805a524130a5ec313871147f7aa9b5318
Gitweb:     http://git.kernel.org/tip/40814f6805a524130a5ec313871147f7aa9b5318
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Mon, 19 May 2014 20:41:36 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 5 Jun 2014 12:30:11 +0200

uprobes: Teach copy_insn() to support tmpfs

tmpfs is widely used but as Denys reports shmem_aops doesn't have
->readpage() and thus you can't probe a binary on this filesystem.

As Hugh suggested we can use shmem_read_mapping_page() in this case,
just we need to check shmem_mapping() if ->readpage == NULL.

Reported-by: Denys Vlasenko <dvlasenk@redhat.com>
Suggested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140519184136.GB6750@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/events/uprobes.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c56b13e..6bfb671 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -36,6 +36,7 @@
 #include "../../mm/internal.h"	/* munlock_vma_page */
 #include <linux/percpu-rwsem.h>
 #include <linux/task_work.h>
+#include <linux/shmem_fs.h>
 
 #include <linux/uprobes.h>
 
@@ -537,10 +538,14 @@ static int __copy_insn(struct address_space *mapping, struct file *filp,
 {
 	struct page *page;
 	/*
-	 * Ensure that the page that has the original instruction is
-	 * populated and in page-cache.
+	 * Ensure that the page that has the original instruction is populated
+	 * and in page-cache. If ->readpage == NULL it must be shmem_mapping(),
+	 * see uprobe_register().
 	 */
-	page = read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT, filp);
+	if (mapping->a_ops->readpage)
+		page = read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT, filp);
+	else
+		page = shmem_read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT);
 	if (IS_ERR(page))
 		return PTR_ERR(page);
 
@@ -876,8 +881,8 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
 	if (!uc->handler && !uc->ret_handler)
 		return -EINVAL;
 
-	/* copy_insn()->read_mapping_page() needs ->readpage() */
-	if (!inode->i_mapping->a_ops->readpage)
+	/* copy_insn() uses read_mapping_page() or shmem_read_mapping_page() */
+	if (!inode->i_mapping->a_ops->readpage && !shmem_mapping(inode->i_mapping))
 		return -EIO;
 	/* Racy, just to catch the obvious mistakes */
 	if (offset > i_size_read(inode))

Re: [PATCH] uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()

[Srikar Dronamraju]

* Oleg Nesterov <oleg@redhat.com> [2014-05-19 20:40:54]:

> Sorry for double-posting, but it seems that this patch didn't reach
> lkml. Let me resend it just on case. Plus another patch in reply, on
> top of this change.
> 
> -------------------------------------------------------------------------------
> Subject: [PATCH] uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()
> 
> copy_insn() fails with -EIO if ->readpage == NULL, but this error
> is not propagated unless uprobe_register() path finds ->mm which
> already mmaps this file. In this case (say) "perf record" does not
> actually install the probe, but the user can't know about this.
> 
> Move this check into uprobe_register() so that this problem can be
> detected earlier and reported to user.
> 
> Note: this is still not perfect,
> 
> 	- copy_insn() and arch_uprobe_analyze_insn() should be called
> 	  by uprobe_register() but this is not simple, we need vm_file
> 	  for read_mapping_page() (although perhaps we can pass NULL),
> 	  and we need ->mm for is_64bit_mm() (although this logic is
> 	  broken anyway).
> 
> 	- uprobe_register() should be called by create_trace_uprobe(),
> 	  not by probe_event_enable(), so that an error can be detected
> 	  at "perf probe -x" time. This also needs more changes in the
> 	  core uprobe code, uprobe register/unregister interface was
> 	  poorly designed from the very beginning.
> 
> Reported-by: Denys Vlasenko <dvlasenk@redhat.com>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

-- 
Thanks and Regards
Srikar Dronamraju

[tip:perf/core] uprobes: Shift ->readpage check from __copy_insn( ) to uprobe_register()

[tip-bot for Oleg Nesterov]

Commit-ID:  41ccba029e9492dd0fc1bf5c23b72c6322a6dfe9
Gitweb:     http://git.kernel.org/tip/41ccba029e9492dd0fc1bf5c23b72c6322a6dfe9
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Mon, 19 May 2014 20:40:54 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 5 Jun 2014 12:30:07 +0200

uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()

copy_insn() fails with -EIO if ->readpage == NULL, but this error
is not propagated unless uprobe_register() path finds ->mm which
already mmaps this file. In this case (say) "perf record" does not
actually install the probe, but the user can't know about this.

Move this check into uprobe_register() so that this problem can be
detected earlier and reported to user.

Note: this is still not perfect,

	- copy_insn() and arch_uprobe_analyze_insn() should be called
	  by uprobe_register() but this is not simple, we need vm_file
	  for read_mapping_page() (although perhaps we can pass NULL),
	  and we need ->mm for is_64bit_mm() (although this logic is
	  broken anyway).

	- uprobe_register() should be called by create_trace_uprobe(),
	  not by probe_event_enable(), so that an error can be detected
	  at "perf probe -x" time. This also needs more changes in the
	  core uprobe code, uprobe register/unregister interface was
	  poorly designed from the very beginning.

Reported-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140519184054.GA6750@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/events/uprobes.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 3b02c72..c56b13e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -536,9 +536,6 @@ static int __copy_insn(struct address_space *mapping, struct file *filp,
 			void *insn, int nbytes, loff_t offset)
 {
 	struct page *page;
-
-	if (!mapping->a_ops->readpage)
-		return -EIO;
 	/*
 	 * Ensure that the page that has the original instruction is
 	 * populated and in page-cache.
@@ -879,6 +876,9 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
 	if (!uc->handler && !uc->ret_handler)
 		return -EINVAL;
 
+	/* copy_insn()->read_mapping_page() needs ->readpage() */
+	if (!inode->i_mapping->a_ops->readpage)
+		return -EIO;
 	/* Racy, just to catch the obvious mistakes */
 	if (offset > i_size_read(inode))
 		return -EINVAL;