6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Lynch nathanl@linux.ibm.com
[ Upstream commit 01e346ffefda3a7088afebf02b940614179688e7 ]
rtas_token_to_function() WARNs when passed an invalid token; it's meant to catch bugs in kernel-based users of RTAS functions. However, user space controls the token value passed to rtas_token_to_function() by block_rtas_call(), so user space with sufficient privilege to use sys_rtas() can trigger the warnings at will:
unexpected failed lookup for token 2048 WARNING: CPU: 20 PID: 2247 at arch/powerpc/kernel/rtas.c:556 rtas_token_to_function+0xfc/0x110 ... NIP rtas_token_to_function+0xfc/0x110 LR rtas_token_to_function+0xf8/0x110 Call Trace: rtas_token_to_function+0xf8/0x110 (unreliable) sys_rtas+0x188/0x880 system_call_exception+0x268/0x530 system_call_common+0x160/0x2c4
It's desirable to continue warning on bogus tokens in rtas_token_to_function(). Currently it is used to look up RTAS function descriptors when tracing, where we know there has to have been a successful descriptor lookup by different means already, and it would be a serious inconsistency for the reverse lookup to fail.
So instead of weakening rtas_token_to_function()'s contract by removing the warnings, introduce rtas_token_to_function_untrusted(), which has no opinion on failed lookups. Convert block_rtas_call() and rtas_token_to_function() to use it.
Fixes: 8252b88294d2 ("powerpc/rtas: improve function information lookups") Signed-off-by: Nathan Lynch nathanl@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20231212-papr-sys_rtas-vs-lockdown-v6-1-e9eafd0c8c6c@linu... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kernel/rtas.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c index eddc031c4b95..87d65bdd3eca 100644 --- a/arch/powerpc/kernel/rtas.c +++ b/arch/powerpc/kernel/rtas.c @@ -544,6 +544,21 @@ static int __init rtas_token_to_function_xarray_init(void) } arch_initcall(rtas_token_to_function_xarray_init);
+/* + * For use by sys_rtas(), where the token value is provided by user + * space and we don't want to warn on failed lookups. + */ +static const struct rtas_function *rtas_token_to_function_untrusted(s32 token) +{ + return xa_load(&rtas_token_to_function_xarray, token); +} + +/* + * Reverse lookup for deriving the function descriptor from a + * known-good token value in contexts where the former is not already + * available. @token must be valid, e.g. derived from the result of a + * prior lookup against the function table. + */ static const struct rtas_function *rtas_token_to_function(s32 token) { const struct rtas_function *func; @@ -551,7 +566,7 @@ static const struct rtas_function *rtas_token_to_function(s32 token) if (WARN_ONCE(token < 0, "invalid token %d", token)) return NULL;
- func = xa_load(&rtas_token_to_function_xarray, token); + func = rtas_token_to_function_untrusted(token);
if (WARN_ONCE(!func, "unexpected failed lookup for token %d", token)) return NULL; @@ -1726,7 +1741,7 @@ static bool block_rtas_call(int token, int nargs, * If this token doesn't correspond to a function the kernel * understands, you're not allowed to call it. */ - func = rtas_token_to_function(token); + func = rtas_token_to_function_untrusted(token); if (!func) goto err; /*