| Message ID | 20221124165536.1631325-2-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | implement getrandom() in vDSO | expand |
On Thu, Nov 24 2022 at 17:55, Jason A. Donenfeld wrote: > --- > MAINTAINERS | 1 + > arch/x86/Kconfig | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > arch/x86/include/asm/unistd.h | 1 + > drivers/char/random.c | 59 +++++++++++++++++++++++++ > include/uapi/asm-generic/unistd.h | 7 ++- > kernel/sys_ni.c | 3 ++ > lib/vdso/getrandom.h | 23 ++++++++++ > scripts/checksyscalls.sh | 4 ++ > tools/include/uapi/asm-generic/unistd.h | 7 ++- > 10 files changed, 105 insertions(+), 2 deletions(-) > create mode 100644 lib/vdso/getrandom.h I think I asked for this before: Please split these things properly up. Provide the syscall and then wire it up. > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 67745ceab0db..331e21ba961a 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -59,6 +59,7 @@ config X86 > # > select ACPI_LEGACY_TABLES_LOOKUP if ACPI > select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI > + select ADVISE_SYSCALLS if X86_64 Why is this x86_64 specific? > --- a/arch/x86/include/asm/unistd.h > +++ b/arch/x86/include/asm/unistd.h > @@ -27,6 +27,7 @@ > # define __ARCH_WANT_COMPAT_SYS_PWRITEV64 > # define __ARCH_WANT_COMPAT_SYS_PREADV64V2 > # define __ARCH_WANT_COMPAT_SYS_PWRITEV64V2 > +# define __ARCH_WANT_VGETRANDOM_ALLOC So instead of this define, why can't you do: config VGETRADOM_ALLOC bool select ADVISE_SYSCALLS and then have config GENERIC_VDSO_RANDOM_WHATEVER bool select VGETRANDOM_ALLOC This gives a clear Kconfig dependency instead of the random ADVISE_SYSCALLS select. >--- a/drivers/char/random.c > +++ b/drivers/char/random.c > +#include "../../lib/vdso/getrandom.h" Seriously? include/vdso/ exists for a reason. > +#ifdef __ARCH_WANT_VGETRANDOM_ALLOC > +/* > + * The vgetrandom() function in userspace requires an opaque state, which this > + * function provides to userspace, by mapping a certain number of special pages > + * into the calling process. It takes a hint as to the number of opaque states > + * desired, and returns the number of opaque states actually allocated, the > + * size of each one in bytes, and the address of the first state. As this is a syscall which can be invoked outside of the VDSO, can you please provide proper kernel-doc which explains the arguments, the functionality and the return value? > + */ > +SYSCALL_DEFINE3(vgetrandom_alloc, unsigned int __user *, num, > + unsigned int __user *, size_per_each, unsigned int, flags) > +{ > + size_t alloc_size, num_states; > + unsigned long pages_addr; > + unsigned int num_hint; > + int ret; > + > + if (flags) > + return -EINVAL; > + > + if (get_user(num_hint, num)) > + return -EFAULT; > + > + num_states = clamp_t(size_t, num_hint, 1, (SIZE_MAX & PAGE_MASK) / sizeof(struct vgetrandom_state)); > + alloc_size = PAGE_ALIGN(num_states * sizeof(struct vgetrandom_state)); > + > + if (put_user(alloc_size / sizeof(struct vgetrandom_state), num) || > + put_user(sizeof(struct vgetrandom_state), size_per_each)) > + return -EFAULT; That's a total of four sizeof(struct vgetrandom_state) usage sites. size_t state_size = sizeof(struct vgetrandom_state); perhaps? > diff --git a/lib/vdso/getrandom.h b/lib/vdso/getrandom.h > new file mode 100644 > index 000000000000..c7f727db2aaa > --- /dev/null > +++ b/lib/vdso/getrandom.h Wrong place. See above. > @@ -0,0 +1,23 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. > + */ > + > +#ifndef _VDSO_LIB_GETRANDOM_H > +#define _VDSO_LIB_GETRANDOM_H > + > +#include <crypto/chacha.h> > + > +struct vgetrandom_state { > + union { > + struct { > + u8 batch[CHACHA_BLOCK_SIZE * 3 / 2]; > + u32 key[CHACHA_KEY_SIZE / sizeof(u32)]; > + }; > + u8 batch_key[CHACHA_BLOCK_SIZE * 2]; > + }; > + unsigned long generation; > + u8 pos; > +}; Thanks, tglx
Hi Thomas, Thanks a lot for the thorough review, here, and in the other two emails. I appreciate you taking the time to look at it, and my apologies for parts that are unclear or sloppy or otherwise unpolished. I'll try to make v8 a lot better. Comments inline below: On Fri, Nov 25, 2022 at 09:45:31PM +0100, Thomas Gleixner wrote: > On Thu, Nov 24 2022 at 17:55, Jason A. Donenfeld wrote: > > --- > > MAINTAINERS | 1 + > > arch/x86/Kconfig | 1 + > > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > > arch/x86/include/asm/unistd.h | 1 + > > drivers/char/random.c | 59 +++++++++++++++++++++++++ > > include/uapi/asm-generic/unistd.h | 7 ++- > > kernel/sys_ni.c | 3 ++ > > lib/vdso/getrandom.h | 23 ++++++++++ > > scripts/checksyscalls.sh | 4 ++ > > tools/include/uapi/asm-generic/unistd.h | 7 ++- > > 10 files changed, 105 insertions(+), 2 deletions(-) > > create mode 100644 lib/vdso/getrandom.h > > I think I asked for this before: > > Please split these things properly up. Provide the syscall and then wire > it up. Before I split it into "syscall, generic vdso, x86 vdso", as that's how I interpreted your email. Next, I'll split it up into "generic syscall, generic vdso, x86 vdso & syscall", since enabling the syscall without the vdso function, or vice-versa, doesn't make sense, and having that last step be all at once there will provide an easy thing for other archs to look at. > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index 67745ceab0db..331e21ba961a 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -59,6 +59,7 @@ config X86 > > # > > select ACPI_LEGACY_TABLES_LOOKUP if ACPI > > select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI > > + select ADVISE_SYSCALLS if X86_64 > > Why is this x86_64 specific? > > > --- a/arch/x86/include/asm/unistd.h > > +++ b/arch/x86/include/asm/unistd.h > > @@ -27,6 +27,7 @@ > > # define __ARCH_WANT_COMPAT_SYS_PWRITEV64 > > # define __ARCH_WANT_COMPAT_SYS_PREADV64V2 > > # define __ARCH_WANT_COMPAT_SYS_PWRITEV64V2 > > +# define __ARCH_WANT_VGETRANDOM_ALLOC > > So instead of this define, why can't you do: > > config VGETRADOM_ALLOC > bool > select ADVISE_SYSCALLS > > and then have > > config GENERIC_VDSO_RANDOM_WHATEVER > bool > select VGETRANDOM_ALLOC > > This gives a clear Kconfig dependency instead of the random > ADVISE_SYSCALLS select. That's much better indeed. I was trying to straddle the two conventions of `#define __ARCH_...` for syscalls and a Kconfig for vDSO functions, but doing it all together as you've suggested is nicer. I'll try to figure this out, though so far futzing around suggests there might have to be both, because of unistd.h being a userspace header. That is, include/uapi/asm-generic/unistd.h typically needs a `#if __ARCH_WANT..., #define ...` in it. I'll give it a spin and you'll see for v8. At the very least it should get rid of the more awkward `select ADVISE_SYSCALLS if X86_64` part, and will better separate the arch code from non-arch code. > > >--- a/drivers/char/random.c > > +++ b/drivers/char/random.c > > > +#include "../../lib/vdso/getrandom.h" > > Seriously? > > include/vdso/ exists for a reason. Er, yes, thanks. > > > +#ifdef __ARCH_WANT_VGETRANDOM_ALLOC > > +/* > > + * The vgetrandom() function in userspace requires an opaque state, which this > > + * function provides to userspace, by mapping a certain number of special pages > > + * into the calling process. It takes a hint as to the number of opaque states > > + * desired, and returns the number of opaque states actually allocated, the > > + * size of each one in bytes, and the address of the first state. > > As this is a syscall which can be invoked outside of the VDSO, can you > please provide proper kernel-doc which explains the arguments, the > functionality and the return value? Yes, will do. > > > + */ > > +SYSCALL_DEFINE3(vgetrandom_alloc, unsigned int __user *, num, > > + unsigned int __user *, size_per_each, unsigned int, flags) > > +{ > > + size_t alloc_size, num_states; > > + unsigned long pages_addr; > > + unsigned int num_hint; > > + int ret; > > + > > + if (flags) > > + return -EINVAL; > > + > > + if (get_user(num_hint, num)) > > + return -EFAULT; > > + > > + num_states = clamp_t(size_t, num_hint, 1, (SIZE_MAX & PAGE_MASK) / sizeof(struct vgetrandom_state)); > > + alloc_size = PAGE_ALIGN(num_states * sizeof(struct vgetrandom_state)); > > + > > + if (put_user(alloc_size / sizeof(struct vgetrandom_state), num) || > > + put_user(sizeof(struct vgetrandom_state), size_per_each)) > > + return -EFAULT; > > That's a total of four sizeof(struct vgetrandom_state) usage sites. > > size_t state_size = sizeof(struct vgetrandom_state); > > perhaps? Not my style -- I like to have the constant expression at the usage site so I don't have to remember the variable -- but I'm fine going with your suggestion, so I'll do that for v8. Jason
On Sun, Nov 27 2022 at 21:18, Jason A. Donenfeld wrote: > On Fri, Nov 25, 2022 at 09:45:31PM +0100, Thomas Gleixner wrote: >> > --- a/arch/x86/include/asm/unistd.h >> > +++ b/arch/x86/include/asm/unistd.h >> > @@ -27,6 +27,7 @@ >> > # define __ARCH_WANT_COMPAT_SYS_PWRITEV64 >> > # define __ARCH_WANT_COMPAT_SYS_PREADV64V2 >> > # define __ARCH_WANT_COMPAT_SYS_PWRITEV64V2 >> > +# define __ARCH_WANT_VGETRANDOM_ALLOC >> >> So instead of this define, why can't you do: >> >> config VGETRADOM_ALLOC >> bool >> select ADVISE_SYSCALLS >> >> and then have >> >> config GENERIC_VDSO_RANDOM_WHATEVER >> bool >> select VGETRANDOM_ALLOC >> >> This gives a clear Kconfig dependency instead of the random >> ADVISE_SYSCALLS select. > > That's much better indeed. I was trying to straddle the two conventions > of `#define __ARCH_...` for syscalls and a Kconfig for vDSO functions, > but doing it all together as you've suggested is nicer. > > I'll try to figure this out, though so far futzing around suggests there > might have to be both, because of unistd.h being a userspace header. > That is, include/uapi/asm-generic/unistd.h typically needs a `#if > __ARCH_WANT..., #define ...` in it. I'll give it a spin and you'll see Bah. Did not think about that user space part... Thanks, tglx
On Sun, Nov 27, 2022, at 21:18, Jason A. Donenfeld wrote: >> >> config GENERIC_VDSO_RANDOM_WHATEVER >> bool >> select VGETRANDOM_ALLOC >> >> This gives a clear Kconfig dependency instead of the random >> ADVISE_SYSCALLS select. > > That's much better indeed. I was trying to straddle the two conventions > of `#define __ARCH_...` for syscalls and a Kconfig for vDSO functions, > but doing it all together as you've suggested is nicer. > > I'll try to figure this out, though so far futzing around suggests there > might have to be both, because of unistd.h being a userspace header. > That is, include/uapi/asm-generic/unistd.h typically needs a `#if > __ARCH_WANT..., #define ...` in it. I'll give it a spin and you'll see > for v8. At the very least it should get rid of the more awkward > `select ADVISE_SYSCALLS if X86_64` part, and will better separate the > arch code from non-arch code. I think you should not need an __ARCH_WANT_SYS_* symbol for this, the only place we actually need them for is the asm-generic/unistd.h header which is still used on a couple of architectures (I have an experimental series for replacing it with a generic syscall.tbl file, but it's not ready for 6.2). In most cases, the __ARCH_WANT_SYS_* symbols are only used for syscalls that are part of the table for old architectures but get skipped on newer targets that always had a replacement syscalls (e.g. getrlimit getting replaced by prlimit64) I think we should just reserve the syscall number for all architectures right away and #define the __NR_* macro. libc will generally need a runtime check anyway, and defining it now avoids the problem of the tables getting out of sync. The Kconfig symbol is fine in this case. Arnd
Hi Arnd, On Mon, Nov 28, 2022 at 02:54:39PM +0100, Arnd Bergmann wrote: > On Sun, Nov 27, 2022, at 21:18, Jason A. Donenfeld wrote: > >> > >> config GENERIC_VDSO_RANDOM_WHATEVER > >> bool > >> select VGETRANDOM_ALLOC > >> > >> This gives a clear Kconfig dependency instead of the random > >> ADVISE_SYSCALLS select. > > > > That's much better indeed. I was trying to straddle the two conventions > > of `#define __ARCH_...` for syscalls and a Kconfig for vDSO functions, > > but doing it all together as you've suggested is nicer. > > > > I'll try to figure this out, though so far futzing around suggests there > > might have to be both, because of unistd.h being a userspace header. > > That is, include/uapi/asm-generic/unistd.h typically needs a `#if > > __ARCH_WANT..., #define ...` in it. I'll give it a spin and you'll see > > for v8. At the very least it should get rid of the more awkward > > `select ADVISE_SYSCALLS if X86_64` part, and will better separate the > > arch code from non-arch code. > > I think you should not need an __ARCH_WANT_SYS_* symbol for this, > the only place we actually need them for is the asm-generic/unistd.h > header which is still used on a couple of architectures (I have > an experimental series for replacing it with a generic syscall.tbl > file, but it's not ready for 6.2). In most cases, the __ARCH_WANT_SYS_* > symbols are only used for syscalls that are part of the table for > old architectures but get skipped on newer targets that always had > a replacement syscalls (e.g. getrlimit getting replaced by prlimit64) > > I think we should just reserve the syscall number for all architectures > right away and #define the __NR_* macro. libc will generally need > a runtime check anyway, and defining it now avoids the problem of > the tables getting out of sync. > > The Kconfig symbol is fine in this case. Oh, great, okay. I'll get rid of the __ARCH stuff entirely then. I jumped the gun and posted v8 earlier today, but I'll include this in a v9, whenever it makes sense to send that. So when reading v8, just assume all he __ARCH_WANT_SYS_* business has been removed. Jason
diff --git a/MAINTAINERS b/MAINTAINERS index 256f03904987..843dd6a49538 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -17287,6 +17287,7 @@ T: git https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git S: Maintained F: drivers/char/random.c F: drivers/virt/vmgenid.c +F: lib/vdso/getrandom.h RAPIDIO SUBSYSTEM M: Matt Porter <mporter@kernel.crashing.org> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 67745ceab0db..331e21ba961a 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -59,6 +59,7 @@ config X86 # select ACPI_LEGACY_TABLES_LOOKUP if ACPI select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI + select ADVISE_SYSCALLS if X86_64 select ARCH_32BIT_OFF_T if X86_32 select ARCH_CLOCKSOURCE_INIT select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index c84d12608cd2..0186f173f0e8 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -372,6 +372,7 @@ 448 common process_mrelease sys_process_mrelease 449 common futex_waitv sys_futex_waitv 450 common set_mempolicy_home_node sys_set_mempolicy_home_node +451 common vgetrandom_alloc sys_vgetrandom_alloc # # Due to a historical design error, certain syscalls are numbered differently diff --git a/arch/x86/include/asm/unistd.h b/arch/x86/include/asm/unistd.h index 761173ccc33c..1bf509eaeff1 100644 --- a/arch/x86/include/asm/unistd.h +++ b/arch/x86/include/asm/unistd.h @@ -27,6 +27,7 @@ # define __ARCH_WANT_COMPAT_SYS_PWRITEV64 # define __ARCH_WANT_COMPAT_SYS_PREADV64V2 # define __ARCH_WANT_COMPAT_SYS_PWRITEV64V2 +# define __ARCH_WANT_VGETRANDOM_ALLOC # define X32_NR_syscalls (__NR_x32_syscalls) # define IA32_NR_syscalls (__NR_ia32_syscalls) diff --git a/drivers/char/random.c b/drivers/char/random.c index a2a18bd3d7d7..71db7b787a60 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -8,6 +8,7 @@ * into roughly six sections, each with a section header: * * - Initialization and readiness waiting. + * - vDSO support helpers. * - Fast key erasure RNG, the "crng". * - Entropy accumulation and extraction routines. * - Entropy collection routines. @@ -39,6 +40,7 @@ #include <linux/blkdev.h> #include <linux/interrupt.h> #include <linux/mm.h> +#include <linux/mman.h> #include <linux/nodemask.h> #include <linux/spinlock.h> #include <linux/kthread.h> @@ -59,6 +61,7 @@ #include <asm/irq.h> #include <asm/irq_regs.h> #include <asm/io.h> +#include "../../lib/vdso/getrandom.h" /********************************************************************* * @@ -167,6 +170,62 @@ int __cold execute_with_initialized_rng(struct notifier_block *nb) __func__, (void *)_RET_IP_, crng_init) + +/******************************************************************** + * + * vDSO support helpers. + * + * The actual vDSO function is defined over in lib/vdso/getrandom.c, + * but this section contains the kernel-mode helpers to support that. + * + ********************************************************************/ + +#ifdef __ARCH_WANT_VGETRANDOM_ALLOC +/* + * The vgetrandom() function in userspace requires an opaque state, which this + * function provides to userspace, by mapping a certain number of special pages + * into the calling process. It takes a hint as to the number of opaque states + * desired, and returns the number of opaque states actually allocated, the + * size of each one in bytes, and the address of the first state. + */ +SYSCALL_DEFINE3(vgetrandom_alloc, unsigned int __user *, num, + unsigned int __user *, size_per_each, unsigned int, flags) +{ + size_t alloc_size, num_states; + unsigned long pages_addr; + unsigned int num_hint; + int ret; + + if (flags) + return -EINVAL; + + if (get_user(num_hint, num)) + return -EFAULT; + + num_states = clamp_t(size_t, num_hint, 1, (SIZE_MAX & PAGE_MASK) / sizeof(struct vgetrandom_state)); + alloc_size = PAGE_ALIGN(num_states * sizeof(struct vgetrandom_state)); + + if (put_user(alloc_size / sizeof(struct vgetrandom_state), num) || + put_user(sizeof(struct vgetrandom_state), size_per_each)) + return -EFAULT; + + pages_addr = vm_mmap(NULL, 0, alloc_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_LOCKED, 0); + if (IS_ERR_VALUE(pages_addr)) + return pages_addr; + + ret = do_madvise(current->mm, pages_addr, alloc_size, MADV_WIPEONFORK); + if (ret < 0) + goto err_unmap; + + return pages_addr; + +err_unmap: + vm_munmap(pages_addr, alloc_size); + return ret; +} +#endif + /********************************************************************* * * Fast key erasure RNG, the "crng". diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 45fa180cc56a..77b6debe7e18 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -886,8 +886,13 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv) #define __NR_set_mempolicy_home_node 450 __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node) +#ifdef __ARCH_WANT_VGETRANDOM_ALLOC +#define __NR_vgetrandom_alloc 451 +__SYSCALL(__NR_vgetrandom_alloc, sys_vgetrandom_alloc) +#endif + #undef __NR_syscalls -#define __NR_syscalls 451 +#define __NR_syscalls 452 /* * 32 bit systems traditionally used different diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 860b2dcf3ac4..f28196cb919b 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -360,6 +360,9 @@ COND_SYSCALL(pkey_free); /* memfd_secret */ COND_SYSCALL(memfd_secret); +/* random */ +COND_SYSCALL(vgetrandom_alloc); + /* * Architecture specific weak syscall entries. */ diff --git a/lib/vdso/getrandom.h b/lib/vdso/getrandom.h new file mode 100644 index 000000000000..c7f727db2aaa --- /dev/null +++ b/lib/vdso/getrandom.h @@ -0,0 +1,23 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. + */ + +#ifndef _VDSO_LIB_GETRANDOM_H +#define _VDSO_LIB_GETRANDOM_H + +#include <crypto/chacha.h> + +struct vgetrandom_state { + union { + struct { + u8 batch[CHACHA_BLOCK_SIZE * 3 / 2]; + u32 key[CHACHA_KEY_SIZE / sizeof(u32)]; + }; + u8 batch_key[CHACHA_BLOCK_SIZE * 2]; + }; + unsigned long generation; + u8 pos; +}; + +#endif /* _VDSO_LIB_GETRANDOM_H */ diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh index f33e61aca93d..7f7928c6487f 100755 --- a/scripts/checksyscalls.sh +++ b/scripts/checksyscalls.sh @@ -44,6 +44,10 @@ cat << EOF #define __IGNORE_memfd_secret #endif +#ifndef __ARCH_WANT_VGETRANDOM_ALLOC +#define __IGNORE_vgetrandom_alloc +#endif + /* Missing flags argument */ #define __IGNORE_renameat /* renameat2 */ diff --git a/tools/include/uapi/asm-generic/unistd.h b/tools/include/uapi/asm-generic/unistd.h index 45fa180cc56a..77b6debe7e18 100644 --- a/tools/include/uapi/asm-generic/unistd.h +++ b/tools/include/uapi/asm-generic/unistd.h @@ -886,8 +886,13 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv) #define __NR_set_mempolicy_home_node 450 __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node) +#ifdef __ARCH_WANT_VGETRANDOM_ALLOC +#define __NR_vgetrandom_alloc 451 +__SYSCALL(__NR_vgetrandom_alloc, sys_vgetrandom_alloc) +#endif + #undef __NR_syscalls -#define __NR_syscalls 451 +#define __NR_syscalls 452 /* * 32 bit systems traditionally used different
The vDSO getrandom() works over an opaque per-thread state of an unexported size, which must be marked as MADV_WIPEONFORK and be mlock()'d for proper operation. Over time, the nuances of these allocations may change or grow or even differ based on architectural features. The syscall has the signature: void *vgetrandom_alloc([inout] unsigned int *num, [out] unsigned int *size_per_each, unsigned int flags); This takes the desired number of opaque states in `num`, and returns a pointer to an array of opaque states, the number actually allocated back in `num`, and the size in bytes of each one in `size_per_each`, enabling a libc to slice up the returned array into a state per each thread. (The `flags` argument is always zero for now.) Libc is expected to allocate a chunk of these on first use, and then dole them out to threads as they're created, allocating more when needed. The following commit shows an example of this, being used in conjunction with the getrandom() vDSO function. We very intentionally do *not* leave state allocation for vDSO getrandom() up to userspace itself, but rather provide this new syscall for such allocations. vDSO getrandom() must not store its state in just any old memory address, but rather just ones that the kernel specially allocates for it, leaving the particularities of those allocations up to the kernel. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- MAINTAINERS | 1 + arch/x86/Kconfig | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/x86/include/asm/unistd.h | 1 + drivers/char/random.c | 59 +++++++++++++++++++++++++ include/uapi/asm-generic/unistd.h | 7 ++- kernel/sys_ni.c | 3 ++ lib/vdso/getrandom.h | 23 ++++++++++ scripts/checksyscalls.sh | 4 ++ tools/include/uapi/asm-generic/unistd.h | 7 ++- 10 files changed, 105 insertions(+), 2 deletions(-) create mode 100644 lib/vdso/getrandom.h