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d4d8c6e6fd
inet_ehashfn() and inet6_ehashfn() initialise random secrets
on the first call by net_get_random_once().
While the init part is patched out using static keys, with
CONFIG_STACKPROTECTOR_STRONG=y, this causes a compiler to
generate a stack canary due to an automatic variable,
unsigned long ___flags, in the DO_ONCE() macro being passed
to __do_once_start().
With FDO, this is visible in __inet_lookup_established() and
__inet6_lookup_established() too.
Let's initialise the secrets by get_random_sleepable_once()
in the slow paths: inet_hash() for listen(), and
inet_hash_connect() and inet6_hash_connect() for connect().
Note that IPv6 listener will initialise both IPv4 & IPv6 secrets
in inet_hash() for IPv4-mapped IPv6 address.
With the patch, the stack size is reduced by 16 bytes (___flags
+ a stack canary) and NOPs for the static key go away.
Before: __inet6_lookup_established()
...
push %rbx
sub $0x38,%rsp # stack is 56 bytes
mov %edx,%ebx # sport
mov %gs:0x299419f(%rip),%rax # load stack canary
mov %rax,0x30(%rsp) and store it onto stack
mov 0x440(%rdi),%r15 # net->ipv4.tcp_death_row.hashinfo
nop
32: mov %r8d,%ebp # hnum
shl $0x10,%ebp # hnum << 16
nop
3d: mov 0x70(%rsp),%r14d # sdif
or %ebx,%ebp # INET_COMBINED_PORTS(sport, hnum)
mov 0x11a8382(%rip),%eax # inet6_ehashfn() ...
After: __inet6_lookup_established()
...
push %rbx
sub $0x28,%rsp # stack is 40 bytes
mov 0x60(%rsp),%ebp # sdif
mov %r8d,%r14d # hnum
shl $0x10,%r14d # hnum << 16
or %edx,%r14d # INET_COMBINED_PORTS(sport, hnum)
mov 0x440(%rdi),%rax # net->ipv4.tcp_death_row.hashinfo
mov 0x1194f09(%rip),%r10d # inet6_ehashfn() ...
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260303235424.3877267-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>