[PATCH v3 1/5] x86/sgx: Fix a resource leak in sgx_init()

[PATCH v3 1/5] x86/sgx: Fix a resource leak in sgx_init()

[Jarkko Sakkinen]

If sgx_page_cache_init() fails in the middle, a trivial return statement
causes unused memory and virtual address space reserved for the EPC
section, not freed. Fix this by using the same rollback, as when
sgx_page_reclaimer_init() fails.

Cc: stable@vger.kernel.org # 5.11
Fixes: e7e0545299d8 ("x86/sgx: Initialize metadata for Enclave Page Cache (EPC) sections")
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 arch/x86/kernel/cpu/sgx/main.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 8df81a3ed945..52d070fb4c9a 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -708,8 +708,10 @@ static int __init sgx_init(void)
 	if (!cpu_feature_enabled(X86_FEATURE_SGX))
 		return -ENODEV;
 
-	if (!sgx_page_cache_init())
-		return -ENOMEM;
+	if (!sgx_page_cache_init()) {
+		ret = -ENOMEM;
+		goto err_page_cache;
+	}
 
 	if (!sgx_page_reclaimer_init()) {
 		ret = -ENOMEM;
-- 
2.30.1

Re: [PATCH v3 1/5] x86/sgx: Fix a resource leak in sgx_init()

[Dave Hansen]

On 3/3/21 7:03 AM, Jarkko Sakkinen wrote:
> If sgx_page_cache_init() fails in the middle, a trivial return
> statement causes unused memory and virtual address space reserved for
> the EPC section, not freed. Fix this by using the same rollback, as
> when sgx_page_reclaimer_init() fails.
...
> @@ -708,8 +708,10 @@ static int __init sgx_init(void)
>  	if (!cpu_feature_enabled(X86_FEATURE_SGX))
>  		return -ENODEV;
>  
> -	if (!sgx_page_cache_init())
> -		return -ENOMEM;
> +	if (!sgx_page_cache_init()) {
> +		ret = -ENOMEM;
> +		goto err_page_cache;
> +	}


Currently, the only way sgx_page_cache_init() can fail is in the case
that there are no sections:

        if (!sgx_nr_epc_sections) {
                pr_err("There are zero EPC sections.\n");
                return false;
        }

That only happened if all sgx_setup_epc_section() calls failed.
sgx_setup_epc_section() never both allocates memory with vmalloc for
section->pages *and* fails.  If sgx_setup_epc_section() has a successful
memremap() but a failed vmalloc(), it cleans up with memunmap().

In other words, I see how this _looks_ like a memory leak from
sgx_init(), but I don't see an actual leak in practice.

Am I missing something?

Re: [PATCH v3 1/5] x86/sgx: Fix a resource leak in sgx_init()

[Jarkko Sakkinen]

On Wed, Mar 03, 2021 at 08:56:52AM -0800, Dave Hansen wrote:
> On 3/3/21 7:03 AM, Jarkko Sakkinen wrote:
> > If sgx_page_cache_init() fails in the middle, a trivial return
> > statement causes unused memory and virtual address space reserved for
> > the EPC section, not freed. Fix this by using the same rollback, as
> > when sgx_page_reclaimer_init() fails.
> ...
> > @@ -708,8 +708,10 @@ static int __init sgx_init(void)
> >  	if (!cpu_feature_enabled(X86_FEATURE_SGX))
> >  		return -ENODEV;
> >  
> > -	if (!sgx_page_cache_init())
> > -		return -ENOMEM;
> > +	if (!sgx_page_cache_init()) {
> > +		ret = -ENOMEM;
> > +		goto err_page_cache;
> > +	}
> 
> 
> Currently, the only way sgx_page_cache_init() can fail is in the case
> that there are no sections:
> 
>         if (!sgx_nr_epc_sections) {
>                 pr_err("There are zero EPC sections.\n");
>                 return false;
>         }
> 
> That only happened if all sgx_setup_epc_section() calls failed.
> sgx_setup_epc_section() never both allocates memory with vmalloc for
> section->pages *and* fails.  If sgx_setup_epc_section() has a successful
> memremap() but a failed vmalloc(), it cleans up with memunmap().
> 
> In other words, I see how this _looks_ like a memory leak from
> sgx_init(), but I don't see an actual leak in practice.
> 
> Am I missing something?

In sgx_setup_epc_section():


	section->pages = vmalloc(nr_pages * sizeof(struct sgx_epc_page));
	if (!section->pages) {
		memunmap(section->virt_addr);
		return false;
	}

I.e. this rollback does not happen without this fix applied:

	for (i = 0; i < sgx_nr_epc_sections; i++) {
		vfree(sgx_epc_sections[i].pages);
		memunmap(sgx_epc_sections[i].virt_addr);
	}

/Jarkko

Re: [PATCH v3 1/5] x86/sgx: Fix a resource leak in sgx_init()

[Sean Christopherson]

On Wed, Mar 10, 2021, Jarkko Sakkinen wrote:
> On Wed, Mar 03, 2021 at 08:56:52AM -0800, Dave Hansen wrote:
> > On 3/3/21 7:03 AM, Jarkko Sakkinen wrote:
> > > If sgx_page_cache_init() fails in the middle, a trivial return
> > > statement causes unused memory and virtual address space reserved for
> > > the EPC section, not freed. Fix this by using the same rollback, as
> > > when sgx_page_reclaimer_init() fails.
> > ...
> > > @@ -708,8 +708,10 @@ static int __init sgx_init(void)
> > >  	if (!cpu_feature_enabled(X86_FEATURE_SGX))
> > >  		return -ENODEV;
> > >  
> > > -	if (!sgx_page_cache_init())
> > > -		return -ENOMEM;
> > > +	if (!sgx_page_cache_init()) {
> > > +		ret = -ENOMEM;
> > > +		goto err_page_cache;
> > > +	}
> > 
> > 
> > Currently, the only way sgx_page_cache_init() can fail is in the case
> > that there are no sections:
> > 
> >         if (!sgx_nr_epc_sections) {
> >                 pr_err("There are zero EPC sections.\n");
> >                 return false;
> >         }
> > 
> > That only happened if all sgx_setup_epc_section() calls failed.
> > sgx_setup_epc_section() never both allocates memory with vmalloc for
> > section->pages *and* fails.  If sgx_setup_epc_section() has a successful
> > memremap() but a failed vmalloc(), it cleans up with memunmap().
> > 
> > In other words, I see how this _looks_ like a memory leak from
> > sgx_init(), but I don't see an actual leak in practice.
> > 
> > Am I missing something?
> 
> In sgx_setup_epc_section():
> 
> 
> 	section->pages = vmalloc(nr_pages * sizeof(struct sgx_epc_page));
> 	if (!section->pages) {
> 		memunmap(section->virt_addr);
> 		return false;
> 	}
> 
> I.e. this rollback does not happen without this fix applied:
> 
> 	for (i = 0; i < sgx_nr_epc_sections; i++) {
> 		vfree(sgx_epc_sections[i].pages);
> 		memunmap(sgx_epc_sections[i].virt_addr);
> 	}

Dave is pointing out that sgx_page_cache_init() fails if and only if _all_
sections fail sgx_setup_epc_section(), and if all sections fail then
sgx_nr_epc_sections is '0' and the above is a nop.

That behavior is by design, as we didn't want to kill SGX if a single section
failed to initialize for whatever reason.

Re: [PATCH v3 1/5] x86/sgx: Fix a resource leak in sgx_init()

[Jarkko Sakkinen]

On Wed, Mar 10, 2021 at 07:49:29AM -0800, Sean Christopherson wrote:
> On Wed, Mar 10, 2021, Jarkko Sakkinen wrote:
> > On Wed, Mar 03, 2021 at 08:56:52AM -0800, Dave Hansen wrote:
> > > On 3/3/21 7:03 AM, Jarkko Sakkinen wrote:
> > > > If sgx_page_cache_init() fails in the middle, a trivial return
> > > > statement causes unused memory and virtual address space reserved for
> > > > the EPC section, not freed. Fix this by using the same rollback, as
> > > > when sgx_page_reclaimer_init() fails.
> > > ...
> > > > @@ -708,8 +708,10 @@ static int __init sgx_init(void)
> > > >  	if (!cpu_feature_enabled(X86_FEATURE_SGX))
> > > >  		return -ENODEV;
> > > >  
> > > > -	if (!sgx_page_cache_init())
> > > > -		return -ENOMEM;
> > > > +	if (!sgx_page_cache_init()) {
> > > > +		ret = -ENOMEM;
> > > > +		goto err_page_cache;
> > > > +	}
> > > 
> > > 
> > > Currently, the only way sgx_page_cache_init() can fail is in the case
> > > that there are no sections:
> > > 
> > >         if (!sgx_nr_epc_sections) {
> > >                 pr_err("There are zero EPC sections.\n");
> > >                 return false;
> > >         }
> > > 
> > > That only happened if all sgx_setup_epc_section() calls failed.
> > > sgx_setup_epc_section() never both allocates memory with vmalloc for
> > > section->pages *and* fails.  If sgx_setup_epc_section() has a successful
> > > memremap() but a failed vmalloc(), it cleans up with memunmap().
> > > 
> > > In other words, I see how this _looks_ like a memory leak from
> > > sgx_init(), but I don't see an actual leak in practice.
> > > 
> > > Am I missing something?
> > 
> > In sgx_setup_epc_section():
> > 
> > 
> > 	section->pages = vmalloc(nr_pages * sizeof(struct sgx_epc_page));
> > 	if (!section->pages) {
> > 		memunmap(section->virt_addr);
> > 		return false;
> > 	}
> > 
> > I.e. this rollback does not happen without this fix applied:
> > 
> > 	for (i = 0; i < sgx_nr_epc_sections; i++) {
> > 		vfree(sgx_epc_sections[i].pages);
> > 		memunmap(sgx_epc_sections[i].virt_addr);
> > 	}
> 
> Dave is pointing out that sgx_page_cache_init() fails if and only if _all_
> sections fail sgx_setup_epc_section(), and if all sections fail then
> sgx_nr_epc_sections is '0' and the above is a nop.
> 
> That behavior is by design, as we didn't want to kill SGX if a single section
> failed to initialize for whatever reason.

My bad. You're correct. I got mixed up by the rollback :-) Thanks!

I'll just drop the whole patch.

/Jarkko