[v2,03/17] vdso: Add __arch_get_k_vdso_rng_data()

Commit Message

Christophe Leroy Aug. 22, 2024, 7:13 a.m. UTC

_vdso_data is specific to x86 and __arch_get_k_vdso_data() is provided
so that all architectures can provide the requested pointer.

Do the same with _vdso_rng_data, provide __arch_get_k_vdso_rng_data()
and don't use x86 _vdso_rng_data directly.

Until now vdso/vsyscall.h was only included by time/vsyscall.c but now
it will also be included in char/random.c, leading to a duplicate
declaration of _vdso_data and _vdso_rng_data.

To fix this issue, move declaration in a C file. vma.c looks like the
most appropriate candidate. Don't need to replace the definitions in
vsyscall.h by declarations as declarations are already in asm/vvar.h

Signed-off-by: Christophe Leroy <[e-mail]>
---
v2: Move x86 DEFINE_VVAR(_vdso_data) and DEFINE_VVAR(_vdso_rng_data) in vma.c
---
 arch/x86/entry/vdso/vma.c            |  3 +++
 arch/x86/include/asm/vdso/vsyscall.h | 10 +++++++---
 drivers/char/random.c                |  5 +++--
 3 files changed, 13 insertions(+), 5 deletions(-)

Comments

Jason A. Donenfeld Aug. 26, 2024, 7:24 a.m. UTC | #1

On Thu, Aug 22, 2024 at 09:13:11AM +0200, Christophe Leroy wrote:
> _vdso_data is specific to x86 and __arch_get_k_vdso_data() is provided
> so that all architectures can provide the requested pointer.
> 
> Do the same with _vdso_rng_data, provide __arch_get_k_vdso_rng_data()
> and don't use x86 _vdso_rng_data directly.
> 
> Until now vdso/vsyscall.h was only included by time/vsyscall.c but now
> it will also be included in char/random.c, leading to a duplicate
> declaration of _vdso_data and _vdso_rng_data.
> 
> To fix this issue, move declaration in a C file. vma.c looks like the
> most appropriate candidate. Don't need to replace the definitions in
> vsyscall.h by declarations as declarations are already in asm/vvar.h
> 
> Signed-off-by: Christophe Leroy <[e-mail]>
> ---
> v2: Move x86 DEFINE_VVAR(_vdso_data) and DEFINE_VVAR(_vdso_rng_data) in vma.c

Thanks, this seems sane to me. I'll apply this now to random.git as a
fix; it should have been done this way before and is going to be a
headache to coordinate later.

Jason

Patch

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 6d83ceb7f1ba..b8fed8b8b9cc 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -38,6 +38,9 @@  struct vdso_data *arch_get_vdso_data(void *vvar_page)
 }
 #undef EMIT_VVAR
 
+DEFINE_VVAR(struct vdso_data, _vdso_data);
+DEFINE_VVAR_SINGLE(struct vdso_rng_data, _vdso_rng_data);
+
 unsigned int vclocks_used __read_mostly;
 
 #if defined(CONFIG_X86_64)
diff --git a/arch/x86/include/asm/vdso/vsyscall.h b/arch/x86/include/asm/vdso/vsyscall.h
index 972415a8be31..67fedf1698b5 100644
--- a/arch/x86/include/asm/vdso/vsyscall.h
+++ b/arch/x86/include/asm/vdso/vsyscall.h
@@ -9,9 +9,6 @@ 
 #include <asm/vgtod.h>
 #include <asm/vvar.h>
 
-DEFINE_VVAR(struct vdso_data, _vdso_data);
-DEFINE_VVAR_SINGLE(struct vdso_rng_data, _vdso_rng_data);
-
 /*
  * Update the vDSO data page to keep in sync with kernel timekeeping.
  */
@@ -22,6 +19,13 @@  struct vdso_data *__x86_get_k_vdso_data(void)
 }
 #define __arch_get_k_vdso_data __x86_get_k_vdso_data
 
+static __always_inline
+struct vdso_rng_data *__x86_get_k_vdso_rng_data(void)
+{
+	return &_vdso_rng_data;
+}
+#define __arch_get_k_vdso_rng_data __x86_get_k_vdso_rng_data
+
 /* The asm-generic header needs to be included after the definitions above */
 #include <asm-generic/vdso/vsyscall.h>
 
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 87fe61295ea1..77968309e2c2 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -59,6 +59,7 @@ 
 #ifdef CONFIG_VDSO_GETRANDOM
 #include <vdso/getrandom.h>
 #include <vdso/datapage.h>
+#include <vdso/vsyscall.h>
 #endif
 #include <asm/archrandom.h>
 #include <asm/processor.h>
@@ -282,7 +283,7 @@  static void crng_reseed(struct work_struct *work)
 	 * is ordered with the write above to base_crng.generation. Pairs with
 	 * the smp_rmb() before the syscall in the vDSO code.
 	 */
-	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
+	smp_store_release(&__arch_get_k_vdso_rng_data()->generation, next_gen + 1);
 #endif
 	if (!static_branch_likely(&crng_is_ready))
 		crng_init = CRNG_READY;
@@ -735,7 +736,7 @@  static void __cold _credit_init_bits(size_t bits)
 			queue_work(system_unbound_wq, &set_ready);
 		atomic_notifier_call_chain(&random_ready_notifier, 0, NULL);
 #ifdef CONFIG_VDSO_GETRANDOM
-		WRITE_ONCE(_vdso_rng_data.is_ready, true);
+		WRITE_ONCE(__arch_get_k_vdso_rng_data()->is_ready, true);
 #endif
 		wake_up_interruptible(&crng_init_wait);
 		kill_fasync(&fasync, SIGIO, POLL_IN);